![Iti’s imposible that both 3 and 4 are correct. We do not need location (where) we need time (when).
Tech Interviews comment by Francisco J. Banda
The Answer to the question 5 is 3rd Choice.
The 4rd (Oracle Forms trigger) is in some way correct, but oracle triggers and Forms triggers are not the
same. This question is about Oracle triggers (not Forms).
Tech Interviews comment by Francisco J. Banda
Hi Ahamed Tharik.N your answer is correct, but also answer number 2 works to be able to see the result
uses SQL>print g_yearly_budget.
Tech Interviews comment by Francisco J. Banda
The answer to the question 13 should be 2.
I fully agree with Francisco J. Banda. For Francisco, your answers are right, just match question numbers.
I tried to do and here is the revised answer list. (T means correct answer choice)
1.)1 : T
2.)2 - 4 : 4 - T
3.)1 : T
4.)(1,3,4) - T
5.)2 - 4 : 4 - T
6.)3 - T
7.)4 - T
8.)2 - 3 - 3 : 3 - T
9.)2 - 4 : 4 - T
10.)(3,4) - 1
11.)1 - [I dont know correct answer]
12.)4 - 3 : 3 - T
13.)1 - ? : 2 - T
Thanks.
Tech Interviews comment by Pranav Vora
1.1
2.4
3.2
4.1,3,5
5.2
6.2,3
7.1
8.3
9.4
10.4
11.4
12.1
13.2
14.4
15.3
16.2
17.2
18.1
19.4
20.3
21.4
22.2
23.4
24.4
25.4
Tech Interviews comment by Arti Shah
The answer to the 23 is 4
Tech Interviews comment by vijay
answer for 22 is 2
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![Tech Interviews comment by vijay
answer for 18 is 1
Tech Interviews comment by oraguru
Right answer to QUS.5 is 4th option coz if end loop is missed in programming it wud through error while
compiling , but if u missed EXIT , the program wud not know where to exit the loop …and loop wud go on
Tech Interviews comment by cobra
1. 1
2. 4
3. 1
4. 1,3,4
5. 2
6. 2,3
7. 4
8. 3
9. 4
10. 1
11. 2
12. 3
13. 2
14.4
15. 3
16. 3
17.2
18. 1
19. 3
20.3
21. 4
22. 2
Tech Interviews comment by aa
}
Set 5 : SQL ,PL/SQL & D2K Interview Questions
[message #27446] Fri, 03 October 2003 03:43
Gurusubramanyam
Messages: 78
1. How to implement ISNUMERIC function in SQL *Plus ?
Method 1:
Select length (translate (trim (column_name),' +-.0123456789',' ')) from dual ;
Will give you a zero if it is a number or greater than zero if not numeric (actually gives the count of non numeric
characters)
Method 2:
select instr(translate('wwww',
'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ',
'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'),'X')
FROM dual;
It returns 0 if it is a number, 1 if it is not.
2. How to Select last N records from a Table?
select * from (select rownum a, CLASS_CODE,CLASS_DESC from clm)
where a > ( select (max(rownum)-10) from clm)
Here N = 10
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![SQL :SQL is the language that provides command to interact with the data in the database. SQL consists of three
components - DDL, DML & DCL.
DDL : DDL comprises commands you can use to create and modify the database structure.
DML : DML comprises commands you can use to add, modify, delete and query data in the database.
DCL : DCL comprises commands you can use to control the user access to the database.
Organizing the Database :
Base Tables : A database comprises base tables, which have the following features :
They physically exist on the disk, Each of them has a unique name & they contain data that is crucial to an organization.
Their attributes have data types such as character, integer, decimal, date and time.
CREATE TABLE : This is a DDL command in SQL that creates a new table in a database.
Syntax : CREATE TABLE table-name (column-name data-type [[size]]
NOT NULL/DEFAULT default-value]]
CHECK (column-name > 0)
UNIQUE (column-name)
PRIMARY KEY (column-name)
FOREIGN KEY (column-name) REFERENCES table-name)
ALTER TABLE : This is a DDL command in SQL that modifies the structure of an existing table.
Syntax : ALTER TABLE table-name
ADD (column-name data-type [[size]] [[NOT NULL DEFAULT]]...)
primary key definition / foreign key definition
DROP PRIMARY KEY / DROP FOREIGN KEY)
DROP TABLE : This is DDL command in SQL that deletes the an existing table. Once you delete a table, all data
contained in it is lost and cannot be recovered. The storage space used by this table is also released.
Syntax : DROP TABLE table-name
Interacting with a Database :
SELECT : This is a DML command in SQL that retrieves data from the database in the form of query results. The
command supports the following keywords and clauses :
FROM This keyword specifies the name of the table.
* This keyword selects all the columns of the table.
WHERE This keyword gives the search condition that specifies the data to be retrieved.
AND This operator is used to combine two or more search conditions.
ORDER BY This keyword sorts the query result on one or more columns.
GROUP BY This keyword groups the query result and lets you generate summary result for each group.
NULL values This value indicates that the data is not present.
Subquery This is the query that is place inside the main query. It passes its query result to the main query.
INSERT : This is a DML command in SQL that you use to add data in rows of a table.
SYNTAX : INSERT INTO table-name (column-names) VALUES (constant/NULL)
UPDATE : This is a DML command in SQL that you use to change data on rows of a table.
Syntax : UPDATE table-name SET column-name-value WHERE condition
DELETE : This is a DML command in SQL that removes one or more rows of data from a table.
Syntax : DELETE FROM table-name WHERE condition.
End-user's View of a Database :
Views : Views are relations that are derived from one or more source tables. Views have the following features:
Views let you restrict the access to data so that end-users see data relevant to them.
Views do not physically exist in the database and only their definition is stored by an RDBMS.
An RDBMS accesses the source tables for data to be retrieved from a view.
Any changes that users make to views do not reflect in the source tables if the view has been created using a Join
condition.
Views created WITH CHECK OPTION allows for an added measure of security in a view. For example, the user will not
be able to insert or update a row that could not be selected by the view-with check option prevents this from happening.
CREATE VIEW : A view can be created using the CREATE VIEW command.
Syntax : CREATE VIEW view-name (column-names) AS query.
Retrieving Data from a View : Once you create a view, you can retrieve data from it using the SELECT command, just
as you do for a table.
Restricting Access to a Database :
GRANT : This is a DCL command in SQL that you use to grant a specific set of authorities to one or more users.
Syntax : GRANT (SQL command) (column-names) ON table-name TO user-name.
REVOKE : This is a DCL command in SQL that you use to take away a specific set of authorities from one or more
users.
Syntax : REVOKE (SQL command) ON table-name TO user-name.
VI. ENSURING INTEGRITY OF DATA :
The concept of Data Integrity :
Data Integrity : Data Integrity refers to the correctness and completeness of data in a database.
Integrity Constraints : Integrity constraints allows only correct changes to be made to a database. There are two types of
integrity constraints - entity integrity and referential integrity.
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![Exception Handlers which is optional.
PL/SQL supports only DML i.e. INSERT, UPDATE, DELETE & SELECT...INTO.
SQL Functions can be referenced within a SQL statement i.e. Numeric (SQRT,ROUND,POWER),
Character (LENGTH,UPPER), DATE (ADD_MONTHS,MONTHS_BETWEEN) &
Group (AVG,MAX,COUNT). Most SQL functions are available outside SQL statement except for group functions.
Code Simple Loops repeats a sequence of statements multiple times.
Syntax : LOOP
<Sequence of Statements>
END LOOP;
Code Numeric FOR Loops repeat a sequence of statements a fixed number of times.
Syntax : FOR <index> IN [[ REVERSE ]] <integer>..<integer> LOOP
<sequence of statements>
END LOOP;
<index> is implicitly of type number. Defined only within the loop & Value can be referenced in an expression, but a new
value cannot be assigned to the index within the loop.
Code While Loops repeats a sequence of statements until a specific condition is no longer TRUE.
Syntax : WHILE <condition> LOOP
<sequence of statements>
END LOOP;
<condition> can be any legal PL/SQL condition & statements will be repeated as long as condition evaluates to TRUE.
Code GOTO Statements jumps to a different place in the PL/SQL block.
Syntax : GOTO label_name;
Legally use a GOTO a statement that is in the same sequence of statements as the GOTO.
In the sequence of statements that encloses the GOTO statement (outer block).
Labels can label any statement. Used as targets for GOTO statements, use labels for blocks and loops, Label a block to
allow referencing of DECLAREd objects that would otherwise not be visible because of scoping rules, Label a block to
allow a variable to be referenced that might be hidden by a column name, Label a loop to allow an object to be
reference that would otherwise not be visible because of scoping rules & Label an EXIT as a convenient way to specify
exits from outer loops.
Cursors are associated with every SQL DML statement processed by PL/SQL. Two types are Explicit i.e. Multiple row
SELECT statements & Implicit i.e. INSERT, UPDATE, DELETE & SELECT...INTO statements. Implicit cursor is called
the SQL cursor-it stores info concerning the processing of the last SQL statement not associated with an explicit cursor.
OPEN, FETCH & CLOSE do not apply. All cursor attributes apply.
Cursor has to be explicitly defined when a query returns multiple rows to process beyond the first row returned by the
query & to keep track of which row is currently being processed.
Declare the cursor to associate its name with a SELECT statement.
Syntax : DECLARE
CURSOR <cursor_name>
IS <regular_select_statement>;
Open the cursor to process the SELECT statement and store the returned rows in the cursor.
Syntax : OPEN <cursor_name>;
Fetch data from the cursor and store it in specified variables.
Syntax : FETCH <cursor_name> INTO <var1, var2...>;
Close the cursor to free up resources. Cursors must be closed before they can be reopened.
Syntax : CLOSE <cursor_name>
Explicit Cursor Attributes are %NOTFOUND, %FOUND, %ROWCOUNT & %ISOPEN.
Reference the current cursor row with the WHERE CURRENT OF statement. The cursor must be declared with a FOR
UPDATE OF clause.
Syntax : WHERE CURRENT OF <cursor_name>
Reference Cursors FOR Loops to specify a sequence of statements to be repeated once for each row that is returned
by the cursor with the Cursor FOR Loop.
Syntax : FOR <record_name> IN <cursor_name> LOOP
--statements to be repeated go here
END LOOP;
Cursor FOR loops (CFL) are similar to Numeric For Loops(NFL). CFL specify a set of rows from a table using the
cursor's name. NFL specify an integer range. CFL record takes on vales of each row. NFL index takes on each value in
the range. Record_name is implicitly declared as
record_name cursor_name%ROWTYPE
When a CFL is initiated, an implicit OPEN cursor_name is initiated.
For each row that satisfies the query associated with the cursor, an implicit FETCH is executed into the components of
record_name.
When there are no more rows left to FETCH, an implicit CLOSE cursor_name is executed and the loop is exited.
Declare cursors to use parameters
Syntax : DECLARE
CURSOR <cursor_name> [[(param_name param_type)]]
IS <regular select statement>;
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![Yes. With respect to table
ALTER TABLE TABLE
[[ DISABLE all_trigger ]]
34) What is pseudo columns ? Name them?
A pseudocolumn behaves like a table column, but is not actually stored in the table. You can select from
pseudocolumns, but you cannot insert, update, or delete their values. This section describes these pseudocolumns:
* CURRVAL
* NEXTVAL
* LEVEL
* ROWID
* ROWNUM
35) How many columns can table have?
The number of columns in a table can range from 1 to 254.
36) Is space acquired in blocks or extents ?
In extents .
37) what is clustered index?
In an indexed cluster, rows are stored together based on their cluster key values . Can not applied for HASH.
38) what are the datatypes supported By oracle (INTERNAL)?
Varchar2, Number,Char , MLSLABEL.
39 ) What are attributes of cursor?
%FOUND , %NOTFOUND , %ISOPEN,%ROWCOUNT
40) Can you use select in FROM clause of SQL select ?
Yes.
GUI
1) What is a visual attribute?
Visual attributes are the font, color, and pattern properties that you set for form and menu objects that appear in your
application's interface.
2) Diff. between VAT and Property Class? imp
Named visual attributes define only font, color, and pattern attributes; property classes can contain these and any other
properties.You can change the appearance of objects at runtime by changing the named visual attribute
programmatically; property class assignment cannot be changed programmatically. When an object is inheriting from
both a property class and a named visual attribute, the named visual attribute settings take precedence, and any visual
attribute properties in the class are ignored.
3 ) Which trigger related to mouse?
* When-Mouse-Click
* When-Mouse-DoubleClick
* When-Mouse-Down
* When-Mouse-Enter
* When-Mouse-Leave
* When-Mouse-Move
* When-Mouse-Up
4) What is Current record attribute property?
Specifies the named visual attribute used when an item is part of the current record.
Current Record Attribute is frequently used at the block level to display the current row in a multi-record If you define an
item-level Current Record Attribute, you can display a pre-determined item in a special color when it is part of the
current record, but you cannot dynamically highlight the current item, as the input focus changes.
5) Can u change VAT at run time?
Yes. You can programmatically change an object's named visual attribute setting to change the font, color, and pattern
of the object at runtime.
6) Can u set default font in forms?
Yes. Change windows registry(regedit). Set form45_font to the desired font.
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62498 242015-oracle self-development_print
- 1. Oracle Interview Questions : The Interviewer’s Prespective "We're interviewing an Oracle guy tomorrow, can you give me a few questions to ask him?" Not an uncommon request. The problem is, there are literally thousands of potential Oracle questions, but it all depends on what are you trying to achieve. So I pushed back: "What kind of Oracle-related skills would the candidate need that you want to ask for?" "You tell us. We just want to know if he knows Oracle. Whatever an Oracle guy would need to know." Pretty soon thereafter I figured out that it was a pointless conversation to continue, although I did love the way he summarized dozens of very different positions into that one term: "Oracle Guy." Nevertheless, it got me thinking. What makes for a good technical question? I have conducted, or been invited to, several interviews, so it got me to thinking about which questions were most effective at getting to the heart of the matter: "Will this candidate succeed technically in this role?" Elements of a Good Technical Interview Question. 1. Must require knowledge of the area, including domain and philosophy, to solve. I don't think it's enough that a candidate demonstrates proficiency with the technology. I like to see if they understand the overall philosophy of the product (Oracle, in this case): What needs was it meant to provide, what kind of problems was it designed to solve, how does it accomplish those tasks. 2. Must require overall technical skill/experience/understanding to solve. I mean to say that a good question shows if the candidate understands (for example) relational databases themselves, not just a particular relational database. Carrying this example, does your C++ developer understand algorithms and software design? 3. Does not require knowledge of precise syntax In my mind, anyone can look something up in a manual. You don't need to walk into an empty boardroom and know exactly how something is called. I don't think knowledge of syntax is a reliable indicator of the suitability of a candidate. For example, you could have a good candidate "blank out" on the syntactic details, and you could also have a bad candidate who swallowed a reference manual the night before the interview. Now, I would be worried if the candidate didn't know BASIC syntax. But I don't want to waste precious time asking basic questions, and if he is truly is that inexperienced, I should be able to figure it out in other ways. 4. Can be answered quickly. Time is precious in an interview, and you shouldn't need long, convoluted questions to determine whether or not a candidate "gets it." A good question demonstrates quickly if the candidate is on the right path, or wouldn't get it regardless of how much time he had. 5. Is not a "gotcha" I've met some interviewers that seem to use the opportunity not to evaluate the candidate, but to prove how clever they are (either to the candidate or the manager). They do this by asking really obscure tricks, sometimes referred to as "gotchas." The problem with asking questions in the obscure corners is that even very experienced candidates may not have worked in that area and, if they have, may not have stumbled across that particular gem. Just remember, the purpose of the interview isn't to make YOU look clever, and asking silly questions might make a great candidate think "what kind of clown show am I getting myself into?" 6. Has many possible solutions and approaches The most effective questions I have ever asked, or been asked, were the ones that triggered lively technical discussions between the interviewer and the candidate. Why? You get to catch a glimpse not only of the candidates thinking process, but also how he communicates. I also like the added benefit of not punishing (in fact, rewarding) those that approach problems differently than the interviewer. Page 1 of 74
- 2. 7. Requires asking for more information (or make assumptions). Personally, I believe one of the keys to success in IT is to define a problem before approaching it. That's why I lean towards these types of questions. Did the candidate come back, or just try to solve it? If he came back, what kind of questions did he ask? In the face of an incompletely-defined problem, did he get stuck, or did he make some assumptions and continue? If so, what assumptions did he make? 8. Is relevant to the business/job being considered Would you hire a cleaning service with award-winning carpet cleaning if you had hardwood floors? Would you hire a running back who excels in bad weather if you played in a dome? Would you hire an accomplished science-fiction writer to author your biography? No? Then why probe for technical skills that don't directly apply to the position you're attempting to fill? Closing Thoughts Incidentally, in the end I referred the manager in question to a couple of links which have hundreds of Oracle-interview questions. You can pick your favourites but, more likely, you can read them until you come up with good ideas that suit your needs. http://www.orafaq.com/forum/t/9760/2/ http://www.databasejournal.com/features/oracle/article.php/3085171 As an aside, that last article was written by one of my preferred columnists, James Koopmann. He hasn't written much recently, but check out his archives, he's got some great articles there. For instance, check out his series on Oracle Session Tracing. Set 1 Oracle Technical Interview Questions Answered – Part1 James Koopmann, jkoopmann@qwest.net The interview process can be quite stressful. Here is the first part of a two part series on helping you answer those tough questions that you might experience in your quest for an Oracle DBA position. Ever since I wrote the past article on the Oracle Technical Interview, I have been bombarded with e-mails asking for help on getting through the interview questions that I presented. Most of you I have answered, others I was reluctant to post all of the answers so that you could begin your own quest for the answers. Now, however, I have decided to post the answers knowing that we can all benefit from them. If there are any questions here that you still need clarification on, please e-mail me and I will do my best to further explain the answer I have given. Please remember that as you go through the article, it is not enough to know the answer to a particular question, you must try and put yourself in an interview situation and experience answering the question for yourself. Therefore, after you have gone through the questions and answers read the question yourself and then answer it with your own words. As always, good luck, and cheers. Personal This part of the interview question is not to be regarded as insignificant. If the interviewer asks you these questions take it as a sign that they are interested in you, your qualities, and how you interact with people throughout the day. Take it as an opportunity to prove that you have been around the block a few times, are willing to work with other people, and enjoy the job you do. Many times people see DBA types as stuffy and pointed, not willing to work with others, and only concerned with the database and its day-to-day operational needs. Put aside the needs of the database and talk about how you work with people and the different departments in the organization and are concerned with providing them with top notch database services. 1. What DBA activities did you to do today? Wow, this is a loaded question and almost begs for you to answer it with "What DBA activities do you LIKE to do on a daily basis?." And that is how I would answer this question. Again, do not get caught up in the "typical" day-to-day operational issues of database administration. Sure, you can talk about the index you rebuilt, the monitoring of system and session waits that were occurring, or the space you added to a data file, these are all good and great and you should convey that you understand the day-to-day operational issues. What you should also throw into this answer are the meetings that you attend to provide direction in the database arena, the people that you meet and talk with daily to answer adhoc questions about database use, the modeling of business needs within the database, and the extra time Page 2 of 74
- 3. you spend early in the morning or late at night to get the job done. Just because the question stipulates "today" do not take "today" to mean "today." Make sure you wrap up a few good days into "today" and talk about them. This question also begs you to ask the question of "What typical DBA activities are performed day to day within X Corporation?" 2. What is your typical day like? If you spend enough time on question 1, this question will never be asked. It is really a continuation of question 1 to try and get you to open up and talk about the type of things you like to do. Personally, I would continue with the theme of question 1 if you are cut short or this question is asked later in the interview process. Just note that this question is not all geared toward the day-to-day operational issues you experience as a DBA. This question also gives you the opportunity to see if they want to know about you as an individual. Since the question did not stipulate "on the job" I would throw in a few items like, I get up at 5:00am to get into work and get some quiet time to read up on new trends or you help coach your son/daughter's soccer team. Just test the waters to what is acceptable. If the interviewer starts to pull you back to "job" related issues, do not go to personal. Also, if you go to the office of the interviewer please notice the surroundings, if there are pictures of his/her family, it is probably a good idea to venture down the personal path. If there is a fly-fishing picture on the wall, do not say you like deep-sea fishing. You get the picture. 3. What other parts of your organization do you interact with and how? Again, if you have exhausted question 1 and 2 you may never get to this question. But if you have been apprehensive to opening up and explaining yourself, take note that you may have an issue and the interviewer might also be already getting tired of the interview process. If you get to this question consider yourself in trouble. You really need to forget all your hang-ups and start explaining what it is that you like to do as a DBA, and why you want to work for this particular company. You are going to have to reel this interviewer back into the interview process or you might not get to the true technical question part of the interview. 4. Do you consider yourself a development DBA or a production DBA and why? I take this as a trick question and explain it that way. Never in my database carrier have I distinguished between "development" and "production." Just ask your development staff or VP of engineering how much time and money is lost if development systems are down. Explain to the interviewer that both systems are equally important to the operation of the company and both should be considered as production systems because there are people relying on them and money is lost if either one of them is down. Ok you may be saying, and I know you are, that we lose more money if the production system is down. Ok, convey that to the interviewer and you won't get anyone to disagree with you unless your company sells software or there are million dollar deals on the table that are expecting the next release of your product or service. 5. Are you a nuts-n-bolts DBA or a tools-n-props DBA This question begs for me to give definition around the terms I basically group DBAs into. These are not good or bad groups but something I like to think about when talking to DBAs. A nuts-n-bolts DBA is the type that likes to figure out every little item about how the database works. He/she is a DBA who typically hates a GUI environment and prefers the command line to execute commands and accomplish tasks. A nuts-n-bolts DBA like to feel in control of the database and only feels comfortable at the command line and vi as an editor. The tools-n-props DBA is mostly the opposite of a nuts-n-bolts DBA, they like the feel of a GUI, the ease at which things can be accomplished without knowing much about the database. They want to get the job done with the least amount of intervention from having to figure out what everything is doing behind the scenes. Now the answer, I would explain myself as a combination of the two. I, having been in this business for over 20 years, have grown up in a command line era where the GUIs never seemed to work. There was high complexity in systems and not much good documentation on how things worked. Thus, I had to learn everything about most aspects of the database environment I was working in and thus became a nuts-n-bolts DBA. I was a true command line and vi bigot. Times have changed and the GUIs are very reliable, understand the environment they are installed on, and can generally get the job done quicker for individuals new to database administration. I too am slowly slipping over to the dark side of GUI administration. If you find yourself as a tools-n-props DBA, try to convey that you are aware of some tasks that require you to be a nuts-n-bolts DBA. Technical – Oracle This is the part you have all been waiting on. Please if you have just skipped to this section, go back to the personal section and read it. There is much to be gained by the personal section and conveying to your interviewer who you are and how you tick from day to day. Also, the answers I am giving here are off the cuff and are not intended to be the definitive answer to these questions. There are many aspects to these questions that just cannot be answered here and honestly, you will not have time to explain any of these questions fully in the interview process. It is up to you to make sure your interviewer understands that you understand the question and have given enough information that they know you understand the concept. 1. Explain the difference between a hot backup and a cold backup and the benefits associated with each. Page 3 of 74
- 4. A hot backup is basically taking a backup of the database while it is still up and running and it must be in archive log mode. A cold backup is taking a backup of the database while it is shut down and does not require being in archive log mode. The benefit of taking a hot backup is that the database is still available for use while the backup is occurring and you can recover the database to any point in time. The benefit of taking a cold backup is that it is typically easier to administer the backup and recovery process. In addition, since you are taking cold backups the database does not require being in archive log mode and thus there will be a slight performance gain as the database is not cutting archive logs to disk. 2. You have just had to restore from backup and do not have any control files. How would you go about bringing up this database? I would create a text based backup control file, stipulating where on disk all the data files where and then issue the recover command with the using backup control file clause. 3. How do you switch from an init.ora file to a spfile? Issue the create spfile from pfile command. 4. Explain the difference between a data block, an extent and a segment. A data block is the smallest unit of logical storage for a database object. As objects grow they take chunks of additional storage that are composed of contiguous data blocks. These groupings of contiguous data blocks are called extents. All the extents that an object takes when grouped together are considered the segment of the database object. 5. Give two examples of how you might determine the structure of the table DEPT. Use the describe command or use the dbms_metadata.get_ddl package. 6. Where would you look for errors from the database engine? In the alert log. 7. Compare and contrast TRUNCATE and DELETE for a table. Both the truncate and delete command have the desired outcome of getting rid of all the rows in a table. The difference between the two is that the truncate command is a DDL operation and just moves the high water mark and produces a now rollback. The delete command, on the other hand, is a DML operation, which will produce a rollback and thus take longer to complete. 8. Give the reasoning behind using an index. Faster access to data blocks in a table. 9. Give the two types of tables involved in producing a star schema and the type of data they hold. Fact tables and dimension tables. A fact table contains measurements while dimension tables will contain data that will help describe the fact tables. 10. . What type of index should you use on a fact table? A Bitmap index. 11. Give two examples of referential integrity constraints. A primary key and a foreign key. 12. A table is classified as a parent table and you want to drop and re-create it. How would you do this without affecting the children tables? Disable the foreign key constraint to the parent, drop the table, re-create the table, enable the foreign key constraint. 13. Explain the difference between ARCHIVELOG mode and NOARCHIVELOG mode and the benefits and disadvantages to each. ARCHIVELOG mode is a mode that you can put the database in for creating a backup of all transactions that have occurred in the database so that you can recover to any point in time. NOARCHIVELOG mode is basically the absence Page 4 of 74
- 5. of ARCHIVELOG mode and has the disadvantage of not being able to recover to any point in time. NOARCHIVELOG mode does have the advantage of not having to write transactions to an archive log and thus increases the performance of the database slightly. 14. What command would you use to create a backup control file? Alter database backup control file to trace. 15. Give the stages of instance startup to a usable state where normal users may access it. STARTUP NOMOUNT - Instance startup STARTUP MOUNT - The database is mounted STARTUP OPEN - The database is opened 16. What column differentiates the V$ views to the GV$ views and how? The INST_ID column which indicates the instance in a RAC environment the information came from. 17. How would you go about generating an EXPLAIN plan? Create a plan table with utlxplan.sql. Use the explain plan set statement_id = 'tst1' into plan_table for a SQL statement Look at the explain plan with utlxplp.sql or utlxpls.sql 18. How would you go about increasing the buffer cache hit ratio? Use the buffer cache advisory over a given workload and then query the v$db_cache_advice table. If a change was necessary then I would use the alter system set db_cache_size command. 19. Explain an ORA-01555 You get this error when you get a snapshot too old within rollback. It can usually be solved by increasing the undo retention or increasing the size of rollbacks. You should also look at the logic involved in the application getting the error message. 20. Explain the difference between $ORACLE_HOME and $ORACLE_BASE. ORACLE_BASE is the root directory for oracle. ORACLE_HOME located beneath ORACLE_BASE is where the oracle products reside. December 12, 2003 Oracle Technical Interview Questions Answered - Part2 By James Koopmann This is the second part of the two part series on helping you answer those tough questions that you might experience in your quest for an Oracle DBA position. The Oracle Technical Interview can be quite daunting. You never quite know what to study for and how to prepare. I am fully aware of this, as I have received many emails since my original article on interview questions was released. While these questions are only guidelines as to what should and more than likely will be asked, I hope that you find some comfort in the review of them. As always, do not just memorize the answers, as there are jewels to be found in the quest of figuring out the answer from the question. As always, remember that as you go through the article, it is not enough to know the answer to a particular question; you must try to put yourself in an interview situation and experience answering the question for yourself. Therefore, after you have gone through the questions and answers read the question again and then answer it with your own words. As always, good luck, and cheers. Technical - Oracle Last time, we answered questions 1 thru 20 of the technical part of the interview. Here are the next 30 in this section. Depending on the mood of the interview and your ability to elaborate on the answer, try to give some insight that you Page 5 of 74
- 6. know more than just the simple answer to some of these questions. Also, be sensitive to the interviewer getting tired of you talking too much. Well here they are. 21. How would you determine the time zone under which a database was operating? select DBTIMEZONE from dual; 22. Explain the use of setting GLOBAL_NAMES equal to TRUE. Setting GLOBAL_NAMES dictates how you might connect to a database. This variable is either TRUE or FALSE and if it is set to TRUE it enforces database links to have the same name as the remote database to which they are linking. 23. What command would you use to encrypt a PL/SQL application? WRAP 24. Explain the difference between a FUNCTION, PROCEDURE and PACKAGE. A function and procedure are the same in that they are intended to be a collection of PL/SQL code that carries a single task. While a procedure does not have to return any values to the calling application, a function will return a single value. A package on the other hand is a collection of functions and procedures that are grouped together based on their commonality to a business function or application. 25. Explain the use of table functions. Table functions are designed to return a set of rows through PL/SQL logic but are intended to be used as a normal table or view in a SQL statement. They are also used to pipeline information in an ETL process. 26. Name three advisory statistics you can collect. Buffer Cache Advice, Segment Level Statistics, & Timed Statistics 27. Where in the Oracle directory tree structure are audit traces placed? In unix $ORACLE_HOME/rdbms/audit, in Windows the event viewer 28. Explain materialized views and how they are used. Materialized views are objects that are reduced sets of information that have been summarized, grouped, or aggregated from base tables. They are typically used in data warehouse or decision support systems. 29. When a user process fails, what background process cleans up after it? PMON 30. What background process refreshes materialized views? The Job Queue Processes. 31. How would you determine what sessions are connected and what resources they are waiting for? Use of V$SESSION and V$SESSION_WAIT 32. Describe what redo logs are. Redo logs are logical and physical structures that are designed to hold all the changes made to a database and are intended to aid in the recovery of a database. 33. How would you force a log switch? ALTER SYSTEM SWITCH LOGFILE; 34. Give two methods you could use to determine what DDL changes have been made. You could use Logminer or Streams 35. What does coalescing a tablespace do? Page 6 of 74
- 7. Coalescing is only valid for dictionary-managed tablespaces and de-fragments space by combining neighboring free extents into large single extents. 36. What is the difference between a TEMPORARY tablespace and a PERMANENT tablespace? A temporary tablespace is used for temporary objects such as sort structures while permanent tablespaces are used to store those objects meant to be used as the true objects of the database. 37. Name a tablespace automatically created when you create a database. The SYSTEM tablespace. 38. When creating a user, what permissions must you grant to allow them to connect to the database? Grant the CONNECT to the user. 39. How do you add a data file to a tablespace? ALTER TABLESPACE <tablespace_name> ADD DATAFILE <datafile_name> SIZE <size> 40. How do you resize a data file? ALTER DATABASE DATAFILE <datafile_name> RESIZE <new_size>; 41. What view would you use to look at the size of a data file? DBA_DATA_FILES 42. What view would you use to determine free space in a tablespace? DBA_FREE_SPACE 43. How would you determine who has added a row to a table? Turn on fine grain auditing for the table. 44. How can you rebuild an index? ALTER INDEX <index_name> REBUILD; 45. Explain what partitioning is and what its benefit is. Partitioning is a method of taking large tables and indexes and splitting them into smaller, more manageable pieces. 46. You have just compiled a PL/SQL package but got errors, how would you view the errors? SHOW ERRORS 47. How can you gather statistics on a table? The ANALYZE command. 48. How can you enable a trace for a session? Use the DBMS_SESSION.SET_SQL_TRACE or Use ALTER SESSION SET SQL_TRACE = TRUE; 49. What is the difference between the SQL*Loader and IMPORT utilities? These two Oracle utilities are used for loading data into the database. The difference is that the import utility relies on the data being produced by another Oracle utility EXPORT while the SQL*Loader utility allows data to be loaded that has been produced by other utilities from different data sources just so long as it conforms to ASCII formatted or delimited files. 50. Name two files used for network connection to a database. TNSNAMES.ORA and SQLNET.ORA Technical - UNIX Every DBA should know something about the operating system that the database will be running on. The questions here are related to UNIX but you should equally be able to answer questions related to common Windows environments. Page 7 of 74
- 8. 1. How do you list the files in an UNIX directory while also showing hidden files? ls -ltra 2. How do you execute a UNIX command in the background? Use the "&" 3. What UNIX command will control the default file permissions when files are created? Umask 4. Explain the read, write, and execute permissions on a UNIX directory. Read allows you to see and list the directory contents. Write allows you to create, edit and delete files and subdirectories in the directory. Execute gives you the previous read/write permissions plus allows you to change into the directory and execute programs or shells from the directory. 5. the difference between a soft link and a hard link? A symbolic (soft) linked file and the targeted file can be located on the same or different file system while for a hard link they must be located on the same file system. 6. Give the command to display space usage on the UNIX file system. df -lk 7. Explain iostat, vmstat and netstat. Iostat reports on terminal, disk and tape I/O activity. Vmstat reports on virtual memory statistics for processes, disk, tape and CPU activity. Netstat reports on the contents of network data structures. 8. How would you change all occurrences of a value using VI? Use :%s/<old>/<new>/g 9. Give two UNIX kernel parameters that effect an Oracle install SHMMAX & SHMMNI 10. Briefly, how do you install Oracle software on UNIX. Basically, set up disks, kernel parameters, and run orainst. I hope that these interview questions were not too hard. Remember these are "core" DBA questions and not necessarily related to the Oracle options that you may encounter in some interviews. Take a close look at the requirements for any job and try to extract questions that interviewers may ask from manuals and real life experiences. For instance, if they are looking for a DBA to run their databases in RAC environments, you should try to determine what hardware and software they are using BEFORE you get to the interview. This would allow you to brush up on particular environments and not be caught off-guard. Good luck! Set 1 Interview Questions for Oracle, DBA, Developer Candidates PL/SQL Questions: 1. Describe the difference between a procedure, function and anonymous pl/sql block. Level: Low Page 8 of 74
- 9. Expected answer : Candidate should mention use of DECLARE statement, a function must return a value while a procedure doesn?t have to. 2. What is a mutating table error and how can you get around it? Level: Intermediate Expected answer: This happens with triggers. It occurs because the trigger is trying to update a row it is currently using. The usual fix involves either use of views or temporary tables so the database is selecting from one while updating the other. 3. Describe the use of %ROWTYPE and %TYPE in PL/SQL Level: Low Expected answer: %ROWTYPE allows you to associate a variable with an entire table row. The %TYPE associates a variable with a single column type. 4. What packages (if any) has Oracle provided for use by developers? Level: Intermediate to high Expected answer: Oracle provides the DBMS_ series of packages. There are many which developers should be aware of such as DBMS_SQL, DBMS_PIPE, DBMS_TRANSACTION, DBMS_LOCK, DBMS_ALERT, DBMS_OUTPUT, DBMS_JOB, DBMS_UTILITY, DBMS_DDL, UTL_FILE. If they can mention a few of these and describe how they used them, even better. If they include the SQL routines provided by Oracle, great, but not really what was asked. 5. Describe the use of PL/SQL tables Level: Intermediate Expected answer: PL/SQL tables are scalar arrays that can be referenced by a binary integer. They can be used to hold values for use in later queries or calculations. In Oracle 8 they will be able to be of the %ROWTYPE designation, or RECORD. 6. When is a declare statement needed ? Level: Low The DECLARE statement is used in PL/SQL anonymous blocks such as with stand alone, non-stored PL/SQL procedures. It must come first in a PL/SQL stand alone file if it is used. 7. In what order should a open/fetch/loop set of commands in a PL/SQL block be implemented if you use the %NOTFOUND cursor variable in the exit when statement? Why? Level: Intermediate Expected answer: OPEN then FETCH then LOOP followed by the exit when. If not specified in this order will result in the final return being done twice because of the way the %NOTFOUND is handled by PL/SQL. 8. What are SQLCODE and SQLERRM and why are they important for PL/SQL developers? Level: Intermediate Expected answer: SQLCODE returns the value of the error number for the last error encountered. The SQLERRM returns the actual error message for the last error encountered. They can be used in exception handling to report, or, store in an error log table, the error that occurred in the code. These are especially useful for the WHEN OTHERS exception. 9. How can you find within a PL/SQL block, if a cursor is open? Level: Low Expected answer: Use the %ISOPEN cursor status variable. 10. How can you generate debugging output from PL/SQL? Level:Intermediate to high Expected answer: Use the DBMS_OUTPUT package. Another possible method is to just use the SHOW ERROR command, but this only shows errors. The DBMS_OUTPUT package can be used to show intermediate results from loops and the status of variables as the procedure is executed. The new package UTL_FILE can also be used. 11. What are the types of triggers? Level:Intermediate to high Page 9 of 74
- 10. Expected Answer: There are 12 types of triggers in PL/SQL that consist of combinations of the BEFORE, AFTER, ROW, TABLE, INSERT, UPDATE, DELETE and ALL key words: BEFORE ALL ROW INSERT AFTER ALL ROW INSERT BEFORE INSERT AFTER INSERT etc. DBA: 1. Give one method for transferring a table from one schema to another: Level:Intermediate Expected Answer: There are several possible methods, export-import, CREATE TABLE... AS SELECT, or COPY. 2. What is the purpose of the IMPORT option IGNORE? What is it?s default setting? Level: Low Expected Answer: The IMPORT IGNORE option tells import to ignore "already exists" errors. If it is not specified the tables that already exist will be skipped. If it is specified, the error is ignored and the tables data will be inserted. The default value is N. 3. You have a rollback segment in a version 7.2 database that has expanded beyond optimal, how can it be restored to optimal? Level: Low Expected answer: Use the ALTER TABLESPACE ..... SHRINK command. 4. If the DEFAULT and TEMPORARY tablespace clauses are left out of a CREATE USER command what happens? Is this bad or good? Why? Level: Low Expected answer: The user is assigned the SYSTEM tablespace as a default and temporary tablespace. This is bad because it causes user objects and temporary segments to be placed into the SYSTEM tablespace resulting in fragmentation and improper table placement (only data dictionary objects and the system rollback segment should be in SYSTEM). 5. What are some of the Oracle provided packages that DBAs should be aware of? Level: Intermediate to High Expected answer: Oracle provides a number of packages in the form of the DBMS_ packages owned by the SYS user. The packages used by DBAs may include: DBMS_SHARED_POOL, DBMS_UTILITY, DBMS_SQL, DBMS_DDL, DBMS_SESSION, DBMS_OUTPUT and DBMS_SNAPSHOT. They may also try to answer with the UTL*.SQL or CAT*.SQL series of SQL procedures. These can be viewed as extra credit but aren?t part of the answer. 6. What happens if the constraint name is left out of a constraint clause? Level: Low Expected answer: The Oracle system will use the default name of SYS_Cxxxx where xxxx is a system generated number. This is bad since it makes tracking which table the constraint belongs to or what the constraint does harder. 7. What happens if a tablespace clause is left off of a primary key constraint clause? Level: Low Expected answer: This results in the index that is automatically generated being placed in then users default tablespace. Since this will usually be the same tablespace as the table is being created in, this can cause serious performance problems. 8. What is the proper method for disabling and re-enabling a primary key constraint? Level: Intermediate Expected answer: You use the ALTER TABLE command for both. However, for the enable clause you must specify the USING INDEX and TABLESPACE clause for primary keys. 9. What happens if a primary key constraint is disabled and then enabled without fully specifying the index clause? Level: Intermediate Page 10 of 74
- 11. Expected answer: The index is created in the user?s default tablespace and all sizing information is lost. Oracle doesn?t store this information as a part of the constraint definition, but only as part of the index definition, when the constraint was disabled the index was dropped and the information is gone. 10. (On UNIX) When should more than one DB writer process be used? How many should be used? Level: High Expected answer: If the UNIX system being used is capable of asynchronous IO then only one is required, if the system is not capable of asynchronous IO then up to twice the number of disks used by Oracle number of DB writers should be specified by use of the db_writers initialization parameter. 11. You are using hot backup without being in archivelog mode, can you recover in the event of a failure? Why or why not? Level: High Expected answer: You can?t use hot backup without being in archivelog mode. So no, you couldn?t recover. 12. What causes the "snapshot too old" error? How can this be prevented or mitigated? Level: Intermediate Expected answer: This is caused by large or long running transactions that have either wrapped onto their own rollback space or have had another transaction write on part of their rollback space. This can be prevented or mitigated by breaking the transaction into a set of smaller transactions or increasing the size of the rollback segments and their extents. 13. How can you tell if a database object is invalid? Level: Low Expected answer: By checking the status column of the DBA_, ALL_ or USER_OBJECTS views, depending upon whether you own or only have permission on the view or are using a DBA account. 14. A user is getting an ORA-00942 error yet you know you have granted them permission on the table, what else should you check? Level: Low Expected answer: You need to check that the user has specified the full name of the object (select empid from scott.emp; instead of select empid from emp;) or has a synonym that points to the object (create synonym emp for scott.emp;) 15. A developer is trying to create a view and the database won?t let him. He has the "DEVELOPER" role which has the "CREATE VIEW" system privilege and SELECT grants on the tables he is using, what is the problem? Level: Intermediate Expected answer: You need to verify the developer has direct grants on all tables used in the view. You can?t create a stored object with grants given through views. 16. If you have an example table, what is the best way to get sizing data for the production table implementation? Level: Intermediate Expected answer: The best way is to analyze the table and then use the data provided in the DBA_TABLES view to get the average row length and other pertinent data for the calculation. The quick and dirty way is to look at the number of blocks the table is actually using and ratio the number of rows in the table to its number of blocks against the number of expected rows. 17. How can you find out how many users are currently logged into the database? How can you find their operating system id? Level: high Expected answer: There are several ways. One is to look at the v$session or v$process views. Another way is to check the current_logins parameter in the v$sysstat view. Another if you are on UNIX is to do a "ps -ef|grep oracle|wc -l? command, but this only works against a single instance installation. 18. A user selects from a sequence and gets back two values, his select is: SELECT pk_seq.nextval FROM dual; Page 11 of 74
- 12. What is the problem? Level: Intermediate Expected answer: Somehow two values have been inserted into the dual table. This table is a single row, single column table that should only have one value in it. 19. How can you determine if an index needs to be dropped and rebuilt? Level: Intermediate Expected answer: Run the ANALYZE INDEX command on the index to validate its structure and then calculate the ratio of LF_BLK_LEN/LF_BLK_LEN+BR_BLK_LEN and if it isn?t near 1.0 (i.e. greater than 0.7 or so) then the index should be rebuilt. Or if the ratio BR_BLK_LEN/ LF_BLK_LEN+BR_BLK_LEN is nearing 0.3. SQL/ SQLPlus 1. How can variables be passed to a SQL routine? Level: Low Expected answer: By use of the & symbol. For passing in variables the numbers 1-8 can be used (&1, &2,...,&8) to pass the values after the command into the SQLPLUS session. To be prompted for a specific variable, place the ampersanded variable in the code itself: "select * from dba_tables where owner=&owner_name;" . Use of double ampersands tells SQLPLUS to resubstitute the value for each subsequent use of the variable, a single ampersand will cause a reprompt for the value unless an ACCEPT statement is used to get the value from the user. 2. You want to include a carriage return/linefeed in your output from a SQL script, how can you do this? Level: Intermediate to high Expected answer: The best method is to use the CHR() function (CHR(10) is a return/linefeed) and the concatenation function "||". Another method, although it is hard to document and isn?t always portable is to use the return/linefeed as a part of a quoted string. 3. How can you call a PL/SQL procedure from SQL? Level: Intermediate Expected answer: By use of the EXECUTE (short form EXEC) command. 4. How do you execute a host operating system command from within SQL? Level: Low Expected answer: By use of the exclamation point "!" (in UNIX and some other OS) or the HOST (HO) command. 5. You want to use SQL to build SQL, what is this called and give an example Level: Intermediate to high Expected answer: This is called dynamic SQL. An example would be: set lines 90 pages 0 termout off feedback off verify off spool drop_all.sql select ?drop user ?||username||? cascade;? from dba_users where username not in ("SYS?,?SYSTEM?); spool off Essentially you are looking to see that they know to include a command (in this case DROP USER...CASCADE;) and that you need to concatenate using the ?||? the values selected from the database. 6. What SQLPlus command is used to format output from a select? Level: low Expected answer: This is best done with the COLUMN command. 7. You want to group the following set of select returns, what can you group on? Max(sum_of_cost), min(sum_of_cost), count(item_no), item_no Level: Intermediate Page 12 of 74
- 13. Expected answer: The only column that can be grouped on is the "item_no" column, the rest have aggregate functions associated with them. 8. What special Oracle feature allows you to specify how the cost based system treats a SQL statement? Level: Intermediate to high Expected answer: The COST based system allows the use of HINTs to control the optimizer path selection. If they can give some example hints such as FIRST ROWS, ALL ROWS, USING INDEX, STAR, even better. 9. You want to determine the location of identical rows in a table before attempting to place a unique index on the table, how can this be done? Level: High Expected answer: Oracle tables always have one guaranteed unique column, the rowid column. If you use a min/max function against your rowid and then select against the proposed primary key you can squeeze out the rowids of the duplicate rows pretty quick. For example: select rowid from emp e where e.rowid > (select min(x.rowid) from emp x where x.emp_no = e.emp_no); In the situation where multiple columns make up the proposed key, they must all be used in the where clause. 10. What is a Cartesian product? Level: Low Expected answer: A Cartesian product is the result of an unrestricted join of two or more tables. The result set of a three table Cartesian product will have x * y * z number of rows where x, y, z correspond to the number of rows in each table involved in the join. 11. You are joining a local and a remote table, the network manager complains about the traffic involved, how can you reduce the network traffic? Level: High Expected answer: Push the processing of the remote data to the remote instance by using a view to pre-select the information for the join. This will result in only the data required for the join being sent across. 12. What is the default ordering of an ORDER BY clause in a SELECT statement? Level: Low Expected answer: Ascending 13. What is tkprof and how is it used? Level: Intermediate to high Expected answer: The tkprof tool is a tuning tool used to determine cpu and execution times for SQL statements. You use it by first setting timed_statistics to true in the initialization file and then turning on tracing for either the entire database via the sql_trace parameter or for the session using the ALTER SESSION command. Once the trace file is generated you run the tkprof tool against the trace file and then look at the output from the tkprof tool. This can also be used to generate explain plan output. 14. What is explain plan and how is it used? Level: Intermediate to high Expected answer: The EXPLAIN PLAN command is a tool to tune SQL statements. To use it you must have an explain_table generated in the user you are running the explain plan for. This is created using the utlxplan.sql script. Once the explain plan table exists you run the explain plan command giving as its argument the SQL statement to be explained. The explain_plan table is then queried to see the execution plan of the statement. Explain plans can also be run using tkprof. 15. How do you set the number of lines on a page of output? The width? Level: Low Page 13 of 74
- 14. Expected answer: The SET command in SQLPLUS is used to control the number of lines generated per page and the width of those lines, for example SET PAGESIZE 60 LINESIZE 80 will generate reports that are 60 lines long with a line width of 80 characters. The PAGESIZE and LINESIZE options can be shortened to PAGES and LINES. 16. How do you prevent output from coming to the screen? Level: Low Expected answer: The SET option TERMOUT controls output to the screen. Setting TERMOUT OFF turns off screen output. This option can be shortened to TERM. 17. How do you prevent Oracle from giving you informational messages during and after a SQL statement execution? Level: Low Expected answer: The SET options FEEDBACK and VERIFY can be set to OFF. 18. How do you generate file output from SQL? Level: Low Expected answer: By use of the SPOOL command Tuning Questions: 1. A tablespace has a table with 30 extents in it. Is this bad? Why or why not. Level: Intermediate Expected answer: Multiple extents in and of themselves aren?t bad. However if you also have chained rows this can hurt performance. 2. How do you set up tablespaces during an Oracle installation? Level: Low Expected answer: You should always attempt to use the Oracle Flexible Architecture standard or another partitioning scheme to ensure proper separation of SYSTEM, ROLLBACK, REDO LOG, DATA, TEMPORARY and INDEX segments. 3. You see multiple fragments in the SYSTEM tablespace, what should you check first? Level: Low Expected answer: Ensure that users don?t have the SYSTEM tablespace as their TEMPORARY or DEFAULT tablespace assignment by checking the DBA_USERS view. 4. What are some indications that you need to increase the SHARED_POOL_SIZE parameter? Level: Intermediate Expected answer: Poor data dictionary or library cache hit ratios, getting error ORA-04031. Another indication is steadily decreasing performance with all other tuning parameters the same. 5. What is the general guideline for sizing db_block_size and db_multi_block_read for an application that does many full table scans? Level: High Expected answer: Oracle almost always reads in 64k chunks. The two should have a product equal to 64 or a multiple of 64. 6. What is the fastest query method for a table? Level: Intermediate Expected answer: Fetch by rowid 7. Explain the use of TKPROF? What initialization parameter should be turned on to get full TKPROF output? Level: High Expected answer: The tkprof tool is a tuning tool used to determine cpu and execution times for SQL statements. You use it by first setting timed_statistics to true in the initialization file and then turning on tracing for either the entire database via the sql_trace parameter or for the session using the ALTER SESSION command. Once the trace file is generated you run the tkprof tool against the trace file and then look at the output from the tkprof tool. This can also be used to generate explain plan output. Page 14 of 74
- 15. 8. When looking at v$sysstat you see that sorts (disk) is high. Is this bad or good? If bad -How do you correct it? Level: Intermediate Expected answer: If you get excessive disk sorts this is bad. This indicates you need to tune the sort area parameters in the initialization files. The major sort are parameter is the SORT_AREA_SIZe parameter. 9. When should you increase copy latches? What parameters control copy latches? Level: high Expected answer: When you get excessive contention for the copy latches as shown by the "redo copy" latch hit ratio. You can increase copy latches via the initialization parameter LOG_SIMULTANEOUS_COPIES to twice the number of CPUs on your system. 10. Where can you get a list of all initialization parameters for your instance? How about an indication if they are default settings or have been changed? Level: Low Expected answer: You can look in the init.ora file for an indication of manually set parameters. For all parameters, their value and whether or not the current value is the default value, look in the v$parameter view. 11. Describe hit ratio as it pertains to the database buffers. What is the difference between instantaneous and cumulative hit ratio and which should be used for tuning? Level: Intermediate Expected answer: The hit ratio is a measure of how many times the database was able to read a value from the buffers verses how many times it had to re-read a data value from the disks. A value greater than 80-90% is good, less could indicate problems. If you simply take the ratio of existing parameters this will be a cumulative value since the database started. If you do a comparison between pairs of readings based on some arbitrary time span, this is the instantaneous ratio for that time span. Generally speaking an instantaneous reading gives more valuable data since it will tell you what your instance is doing for the time it was generated over. 12. Discuss row chaining, how does it happen? How can you reduce it? How do you correct it? Level: high Expected answer: Row chaining occurs when a VARCHAR2 value is updated and the length of the new value is longer than the old value and won?t fit in the remaining block space. This results in the row chaining to another block. It can be reduced by setting the storage parameters on the table to appropriate values. It can be corrected by export and import of the effected table. 13. When looking at the estat events report you see that you are getting busy buffer waits. Is this bad? How can you find what is causing it? Level: high Expected answer: Buffer busy waits could indicate contention in redo, rollback or data blocks. You need to check the v$waitstat view to see what areas are causing the problem. The value of the "count" column tells where the problem is, the "class" column tells you with what. UNDO is rollback segments, DATA is data base buffers. 14. If you see contention for library caches how can you fix it? Level: Intermediate Expected answer: Increase the size of the shared pool. 15. If you see statistics that deal with "undo" what are they really talking about? Level: Intermediate Expected answer: Rollback segments and associated structures. 16. If a tablespace has a default pctincrease of zero what will this cause (in relationship to the smon process)? Level: High Expected answer: The SMON process won?t automatically coalesce its free space fragments. 17. If a tablespace shows excessive fragmentation what are some methods to defragment the tablespace? (7.1,7.2 and 7.3 only) Level: High Page 15 of 74
- 16. Expected answer: In Oracle 7.0 to 7.2 The use of the 'alter session set events 'immediate trace name coalesce level ts#';? command is the easiest way to defragment contiguous free space fragmentation. The ts# parameter corresponds to the ts# value found in the ts$ SYS table. In version 7.3 the ?alter tablespace coalesce;? is best. If the free space isn?t contiguous then export, drop and import of the tablespace contents may be the only way to reclaim non-contiguous free space. 18. How can you tell if a tablespace has excessive fragmentation? Level: Intermediate If a select against the dba_free_space table shows that the count of a tablespaces extents is greater than the count of its data files, then it is fragmented. 19. You see the following on a status report: redo log space requests 23 redo log space wait time 0 Is this something to worry about? What if redo log space wait time is high? How can you fix this? Level: Intermediate Expected answer: Since the wait time is zero, no. If the wait time was high it might indicate a need for more or larger redo logs. 20. What can cause a high value for recursive calls? How can this be fixed? Level: High Expected answer: A high value for recursive calls is cause by improper cursor usage, excessive dynamic space management actions, and or excessive statement re-parses. You need to determine the cause and correct it By either relinking applications to hold cursors, use proper space management techniques (proper storage and sizing) or ensure repeat queries are placed in packages for proper reuse. 21. If you see a pin hit ratio of less than 0.8 in the estat library cache report is this a problem? If so, how do you fix it? Level: Intermediate Expected answer: This indicate that the shared pool may be too small. Increase the shared pool size. 22. If you see the value for reloads is high in the estat library cache report is this a matter for concern? Level: Intermediate Expected answer: Yes, you should strive for zero reloads if possible. If you see excessive reloads then increase the size of the shared pool. 23. You look at the dba_rollback_segs view and see that there is a large number of shrinks and they are of relatively small size, is this a problem? How can it be fixed if it is a problem? Level: High Expected answer: A large number of small shrinks indicates a need to increase the size of the rollback segment extents. Ideally you should have no shrinks or a small number of large shrinks. To fix this just increase the size of the extents and adjust optimal accordingly. 24. You look at the dba_rollback_segs view and see that you have a large number of wraps is this a problem? Level: High Expected answer: A large number of wraps indicates that your extent size for your rollback segments are probably too small. Increase the size of your extents to reduce the number of wraps. You can look at the average transaction size in the same view to get the information on transaction size. 25. In a system with an average of 40 concurrent users you get the following from a query on rollback extents: ROLLBACK CUR EXTENTS --------------------- -------------------------- R01 11 R02 8 R03 12 R04 9 SYSTEM 4 You have room for each to grow by 20 more extents each. Is there a problem? Should you take any action? Page 16 of 74
- 17. Level: Intermediate Expected answer: No there is not a problem. You have 40 extents showing and an average of 40 concurrent users. Since there is plenty of room to grow no action is needed. 26. You see multiple extents in the temporary tablespace. Is this a problem? Level: Intermediate Expected answer: As long as they are all the same size this isn?t a problem. In fact, it can even improve performance since Oracle won?t have to create a new extent when a user needs one. Installation/Configuration 1. Define OFA. Level: Low Expected answer: OFA stands for Optimal Flexible Architecture. It is a method of placing directories and files in an Oracle system so that you get the maximum flexibility for future tuning and file placement. 2. How do you set up your tablespace on installation? Level: Low Expected answer: The answer here should show an understanding of separation of redo and rollback, data and indexes and isolation os SYSTEM tables from other tables. An example would be to specify that at least 7 disks should be used for an Oracle installation so that you can place SYSTEM tablespace on one, redo logs on two (mirrored redo logs) the TEMPORARY tablespace on another, ROLLBACK tablespace on another and still have two for DATA and INDEXES. They should indicate how they will handle archive logs and exports as well. As long as they have a logical plan for combining or further separation more or less disks can be specified. 3. What should be done prior to installing Oracle (for the OS and the disks)? Level: Low Expected Answer: adjust kernel parameters or OS tuning parameters in accordance with installation guide. Be sure enough contiguous disk space is available. 4. You have installed Oracle and you are now setting up the actual instance. You have been waiting an hour for the initialization script to finish, what should you check first to determine if there is a problem? Level: Intermediate to high Expected Answer: Check to make sure that the archiver isn?t stuck. If archive logging is turned on during install a large number of logs will be created. This can fill up your archive log destination causing Oracle to stop to wait for more space. 5. When configuring SQLNET on the server what files must be set up? Level: Intermediate Expected answer: INITIALIZATION file, TNSNAMES.ORA file, SQLNET.ORA file 6. When configuring SQLNET on the client what files need to be set up? Level: Intermediate Expected answer: SQLNET.ORA, TNSNAMES.ORA 7. What must be installed with ODBC on the client in order for it to work with Oracle? Level: Intermediate Expected answer: SQLNET and PROTOCOL (for example: TCPIP adapter) layers of the transport programs. 8. You have just started a new instance with a large SGA on a busy existing server. Performance is terrible, what should you check for? Level: Intermediate Expected answer: The first thing to check with a large SGA is that it isn?t being swapped out. 9. What OS user should be used for the first part of an Oracle installation (on UNIX)? Level: low Page 17 of 74
- 18. Expected answer: You must use root first. 10. When should the default values for Oracle initialization parameters be used as is? Level: Low Expected answer: Never 11. How many control files should you have? Where should they be located? Level: Low Expected answer: At least 2 on separate disk spindles. Be sure they say on separate disks, not just file systems. 12. How many redo logs should you have and how should they be configured for maximum recoverability? Level: Intermediate Expected answer: You should have at least three groups of two redo logs with the two logs each on a separate disk spindle (mirrored by Oracle). The redo logs should not be on raw devices on UNIX if it can be avoided. 13. You have a simple application with no "hot" tables (i.e. uniform IO and access requirements). How many disks should you have assuming standard layout for SYSTEM, USER, TEMP and ROLLBACK tablespaces? Expected answer: At least 7, see disk configuration answer above. Data Modeler: 1. Describe third normal form? Level: Low Expected answer: Something like: In third normal form all attributes in an entity are related to the primary key and only to the primary key 2. Is the following statement true or false: "All relational databases must be in third normal form" Why or why not? Level: Intermediate Expected answer: False. While 3NF is good for logical design most databases, if they have more than just a few tables, will not perform well using full 3NF. Usually some entities will be denormalized in the logical to physical transfer process. 3. What is an ERD? Level: Low Expected answer: An ERD is an Entity-Relationship-Diagram. It is used to show the entities and relationships for a database logical model. 4. Why are recursive relationships bad? How do you resolve them? Level: Intermediate A recursive relationship (one where a table relates to itself) is bad when it is a hard relationship (i.e. neither side is a "may" both are "must") as this can result in it not being possible to put in a top or perhaps a bottom of the table (for example in the EMPLOYEE table you couldn?t put in the PRESIDENT of the company because he has no boss, or the junior janitor because he has no subordinates). These type of relationships are usually resolved by adding a small intersection entity. 5. What does a hard one-to-one relationship mean (one where the relationship on both ends is "must")? Level: Low to intermediate Expected answer: This means the two entities should probably be made into one entity. 6. How should a many-to-many relationship be handled? Level: Intermediate Expected answer: By adding an intersection entity table Page 18 of 74
- 19. 7. What is an artificial (derived) primary key? When should an artificial (or derived) primary key be used? Level: Intermediate Expected answer: A derived key comes from a sequence. Usually it is used when a concatenated key becomes too cumbersome to use as a foreign key. 8. When should you consider denormalization? Level: Intermediate Expected answer: Whenever performance analysis indicates it would be beneficial to do so without compromising data integrity. UNIX: 1. How can you determine the space left in a file system? Level: Low Expected answer: There are several commands to do this: du, df, or bdf 2. How can you determine the number of SQLNET users logged in to the UNIX system? Level: Intermediate Expected answer: SQLNET users will show up with a process unique name that begins with oracle, if you do a ps -ef| grep oracle|wc -l you can get a count of the number of users. 3. What command is used to type files to the screen? Level: Low Expected answer: cat, more, pg 4. What command is used to remove a file? Level: Low Expected answer: rm 5. Can you remove an open file under UNIX? Level: Low Expected answer: yes 6. How do you create a decision tree in a shell script? Level: intermediate Expected answer: depending on shell, usually a case-esac or an if-endif or fi structure 7. What is the purpose of the grep command? Level: Low Expected answer: grep is a string search command that parses the specified string from the specified file or files 8. The system has a program that always includes the word nocomp in its name, how can you determine the number of processes that are using this program? Level: intermediate Expected answer: ps -ef|grep *nocomp*|wc -l 9. What is an inode? Level: Intermediate Expected answer: an inode is a file status indicator. It is stored in both disk and memory and tracts file status. There is one inode for each file on the system. 10. The system administrator tells you that the system hasn?t been rebooted in 6 months, should he be proud of this? Level: High Page 19 of 74
- 20. Expected answer: Maybe. Some UNIX systems don?t clean up well after themselves. Inode problems and dead user processes can accumulate causing possible performance and corruption problems. Most UNIX systems should have a scheduled periodic reboot so file systems can be checked and cleaned and dead or zombie processes cleared out. 11. What is redirection and how is it used? Level: Intermediate Expected answer: redirection is the process by which input or output to or from a process is redirected to another process. This can be done using the pipe symbol "|", the greater than symbol ">" or the "tee" command. This is one of the strengths of UNIX allowing the output from one command to be redirected directly into the input of another command. 12. How can you find dead processes? Level: Intermediate Expected answer: ps -ef|grep zombie -- or -- who -d depending on the system. 13. How can you find all the processes on your system? Level: Low Expected answer: Use the ps command 14. How can you find your id on a system? Level: Low Expected answer: Use the "who am i" command. 15. What is the finger command? Level: Low Expected answer: The finger command uses data in the passwd file to give information on system users. 16. What is the easiest method to create a file on UNIX? Level: Low Expected answer: Use the touch command 17. What does >> do? Level: Intermediate Expected answer: The ">>" redirection symbol appends the output from the command specified into the file specified. The file must already have been created. 18. If you aren?t sure what command does a particular UNIX function what is the best way to determine the command? Expected answer: The UNIX man -k command will search the man pages for the value specified. Review the results from the command to find the command of interest. Oracle Troubleshooting: 1. How can you determine if an Oracle instance is up from the operating system level? Level: Low Expected answer: There are several base Oracle processes that will be running on multi-user operating systems, these will be smon, pmon, dbwr and lgwr. Any answer that has them using their operating system process showing feature to check for these is acceptable. For example, on UNIX a ps -ef|grep dbwr will show what instances are up. 2. Users from the PC clients are getting messages indicating : Level: Low ORA-06114: (Cnct err, can't get err txt. See Servr Msgs & Codes Manual) What could the problem be? Expected answer: The instance name is probably incorrect in their connection string. Page 20 of 74
- 21. 3. Users from the PC clients are getting the following error stack: Level: Low ERROR: ORA-01034: ORACLE not available ORA-07318: smsget: open error when opening sgadef.dbf file. HP-UX Error: 2: No such file or directory What is the probable cause? Expected answer: The Oracle instance is shutdown that they are trying to access, restart the instance. 4. How can you determine if the SQLNET process is running for SQLNET V1? How about V2? Level: Low Expected answer: For SQLNET V1 check for the existence of the orasrv process. You can use the command "tcpctl status" to get a full status of the V1 TCPIP server, other protocols have similar command formats. For SQLNET V2 check for the presence of the LISTENER process(s) or you can issue the command "lsnrctl status". 5. What file will give you Oracle instance status information? Where is it located? Level: Low Expected answer: The alert.ora log. It is located in the directory specified by the background_dump_dest parameter in the v$parameter table. 6. Users aren?t being allowed on the system. The following message is received: Level: Intermediate ORA-00257 archiver is stuck. Connect internal only, until freed What is the problem? Expected answer: The archive destination is probably full, backup the archive logs and remove them and the archiver will re-start. 7. Where would you look to find out if a redo log was corrupted assuming you are using Oracle mirrored redo logs? Level: Intermediate Expected answer: There is no message that comes to the SQLDBA or SRVMGR programs during startup in this situation, you must check the alert.log file for this information. 8. You attempt to add a datafile and get: Level: Intermediate ORA-01118: cannot add anymore datafiles: limit of 40 exceeded What is the problem and how can you fix it? Expected answer: When the database was created the db_files parameter in the initialization file was set to 40. You can shutdown and reset this to a higher value, up to the value of MAX_DATAFILES as specified at database creation. If the MAX_DATAFILES is set to low, you will have to rebuild the control file to increase it before proceeding. 9. You look at your fragmentation report and see that smon hasn?t coalesced any of you tablespaces, even though you know several have large chunks of contiguous free extents. What is the problem? Level: High Expected answer: Check the dba_tablespaces view for the value of pct_increase for the tablespaces. If pct_increase is zero, smon will not coalesce their free space. 10. Your users get the following error: Level: Intermediate ORA-00055 maximum number of DML locks exceeded What is the problem and how do you fix it? Expected answer: The number of DML Locks is set by the initialization parameter DML_LOCKS. If this value is set to low (which it is by default) you will get this error. Increase the value of DML_LOCKS. If you are sure that this is just a temporary problem, you can have them wait and then try again later and the error should clear. Page 21 of 74
- 22. 11. You get a call from you backup DBA while you are on vacation. He has corrupted all of the control files while playing with the ALTER DATABASE BACKUP CONTROLFILE command. What do you do? Level: High Expected answer: As long as all datafiles are safe and he was successful with the BACKUP controlfile command you can do the following: CONNECT INTERNAL STARTUP MOUNT (Take any read-only tablespaces offline before next step ALTER DATABASE DATAFILE .... OFFLINE;) RECOVER DATABASE USING BACKUP CONTROLFILE ALTER DATABASE OPEN RESETLOGS; (bring read-only tablespaces back online) Shutdown and backup the system, then restart If they have a recent output file from the ALTER DATABASE BACKUP CONTROL FILE TO TRACE; command, they can use that to recover as well. If no backup of the control file is available then the following will be required: CONNECT INTERNAL STARTUP NOMOUNT CREATE CONTROL FILE .....; However, they will need to know all of the datafiles, logfiles, and settings for MAXLOGFILES, MAXLOGMEMBERS, MAXLOGHISTORY, MAXDATAFILES for the database to use the command. SET 3 1. To see current user name Sql> show user; 2. Change SQL prompt name SQL> set sqlprompt “Manimara > “ Manimara > Manimara > 3. Switch to DOS prompt SQL> host 4. How do I eliminate the duplicate rows ? SQL> delete from table_name where rowid not in (select max(rowid) from table group by duplicate_values_field_name); or SQL> delete from table_name ta where rowid >(select min(rowid) from table_name tb where ta.dv=tb.dv and .....); Example. Table Emp Empno Ename 101 Scott 102 Jiyo 103 Millor 104 Jiyo 105 Smith delete from emp a where rowid < ( select max(rowid) from emp b where a.ename = b.ename ); The output like, Empno Ename 101 Scott 103 Millor 104 Jiyo 105 Smith 5. How do I display row number with records? To achive this use rownum pseudocolumn with query, like SQL> SQL> select rownum, ename from emp; Output: 1 Scott 2 Millor Page 22 of 74
- 23. 3 Jiyo 4 Smith 6. Display the records between two range select rownum, empno, ename from emp where rowid in (select rowid from emp where rownum <=&upto minus select rowid from emp where rownum<&Start); Enter value for upto: 10 Enter value for Start: 7 ROWNUM EMPNO ENAME --------- --------- ---------- 1 7782 CLARK 2 7788 SCOTT 3 7839 KING 4 7844 TURNER 7. I know the nvl function only allows the same data type(ie. number or char or date Nvl(comm, 0)), if commission is null then the text “Not Applicable” want to display, instead of blank space. How do I write the query? SQL> select nvl(to_char(comm.),'NA') from emp; Output : NVL(TO_CHAR(COMM),'NA') ----------------------- NA 300 500 NA 1400 NA NA 8. Oracle cursor : Implicit & Explicit cursors Oracle uses work areas called private SQL areas to create SQL statements. PL/SQL construct to identify each and every work are used, is called as Cursor. For SQL queries returning a single row, PL/SQL declares all implicit cursors. For queries that returning more than one row, the cursor needs to be explicitly declared. 9. Explicit Cursor attributes There are four cursor attributes used in Oracle cursor_name%Found, cursor_name%NOTFOUND, cursor_name%ROWCOUNT, cursor_name%ISOPEN 10. Implicit Cursor attributes Same as explicit cursor but prefixed by the word SQL SQL%Found, SQL%NOTFOUND, SQL%ROWCOUNT, SQL%ISOPEN Tips : 1. Here SQL%ISOPEN is false, because oracle automatically closed the implicit cursor after executing SQL statements. : 2. All are Boolean attributes. 11. Find out nth highest salary from emp table SELECT DISTINCT (a.sal) FROM EMP A WHERE &N = (SELECT COUNT (DISTINCT (b.sal)) FROM EMP B WHERE a.sal<=b.sal); Enter value for n: 2 SAL --------- 3700 12. To view installed Oracle version information SQL> select banner from v$version; Page 23 of 74
- 24. 13. Display the number value in Words SQL> select sal, (to_char(to_date(sal,'j'), 'jsp')) from emp; the output like, SAL (TO_CHAR(TO_DATE(SAL,'J'),'JSP')) --------- ----------------------------------------------------- 800 eight hundred 1600 one thousand six hundred 1250 one thousand two hundred fifty If you want to add some text like, Rs. Three Thousand only. SQL> select sal "Salary ", (' Rs. '|| (to_char(to_date(sal,'j'), 'Jsp'))|| ' only.')) "Sal in Words" from emp / Salary Sal in Words ------- ------------------------------------------------------ 800 Rs. Eight Hundred only. 1600 Rs. One Thousand Six Hundred only. 1250 Rs. One Thousand Two Hundred Fifty only. 14. Display Odd/ Even number of records Odd number of records: select * from emp where (rowid,1) in (select rowid, mod(rownum,2) from emp); 1 3 5 Even number of records: select * from emp where (rowid,0) in (select rowid, mod(rownum,2) from emp) 2 4 6 15. Which date function returns number value? months_between 16. Any three PL/SQL Exceptions? Too_many_rows, No_Data_Found, Value_Error, Zero_Error, Others 17. What are PL/SQL Cursor Exceptions? Cursor_Already_Open, Invalid_Cursor 18. Other way to replace query result null value with a text SQL> Set NULL ‘N/A’ to reset SQL> Set NULL ‘’ 19. What are the more common pseudo-columns? SYSDATE, USER , UID, CURVAL, NEXTVAL, ROWID, ROWNUM 20. What is the output of SIGN function? 1 for positive value, 0 for Zero, -1 for Negative value. 21. What is the maximum number of triggers, can apply to a single table? 12 triggers. Set 4 : PL/SQL interview questions Which of the following statements is true about implicit cursors? Implicit cursors are used for SQL statements that are not named. Developers should use implicit cursors with great care. Implicit cursors are used in cursor for loops to handle data processing. Implicit cursors are no longer a feature in Oracle. Page 24 of 74
- 25. Which of the following is not a feature of a cursor FOR loop? Record type declaration. Opening and parsing of SQL statements. Fetches records from cursor. Requires exit condition to be defined. A developer would like to use referential datatype declaration on a variable. The variable name is EMPLOYEE_LASTNAME, and the corresponding table and column is EMPLOYEE, and LNAME, respectively. How would the developer define this variable using referential datatypes? Use employee.lname%type. Use employee.lname%rowtype. Look up datatype for EMPLOYEE column on LASTNAME table and use that. Declare it to be type LONG. Which three of the following are implicit cursor attributes? %found %too_many_rows %notfound %rowcount %rowtype If left out, which of the following would cause an infinite loop to occur in a simple loop? LOOP END LOOP IF-THEN EXIT Which line in the following statement will produce an error? cursor action_cursor is select name, rate, action into action_record from action_table; There are no errors in this statement. The command used to open a CURSOR FOR loop is open fetch parse None, cursor for loops handle cursor opening implicitly. What happens when rows are found using a FETCH statement It causes the cursor to close It causes the cursor to open It loads the current row values into variables It creates the variables to hold the current row values Read the following code: CREATE OR REPLACE PROCEDURE find_cpt (v_movie_id {Argument Mode} NUMBER, v_cost_per_ticket {argument mode} NUMBER) IS BEGIN IF v_cost_per_ticket > 8.5 THEN SELECT cost_per_ticket INTO v_cost_per_ticket FROM gross_receipt WHERE movie_id = v_movie_id; END IF; END; Which mode should be used for V_COST_PER_TICKET? IN OUT RETURN IN OUT Page 25 of 74
- 26. Read the following code: CREATE OR REPLACE TRIGGER update_show_gross {trigger information} BEGIN {additional code} END; The trigger code should only execute when the column, COST_PER_TICKET, is greater than $3. Which trigger information will you add? WHEN (new.cost_per_ticket > 3.75) WHEN (:new.cost_per_ticket > 3.75 WHERE (new.cost_per_ticket > 3.75) WHERE (:new.cost_per_ticket > 3.75) What is the maximum number of handlers processed before the PL/SQL block is exited when an exception occurs? Only one All that apply All referenced None For which trigger timing can you reference the NEW and OLD qualifiers? Statement and Row Statement only Row only Oracle Forms trigger Read the following code: CREATE OR REPLACE FUNCTION get_budget(v_studio_id IN NUMBER) RETURN number IS v_yearly_budget NUMBER; BEGIN SELECT yearly_budget INTO v_yearly_budget FROM studio WHERE id = v_studio_id; RETURN v_yearly_budget; END; Which set of statements will successfully invoke this function within SQL*Plus? VARIABLE g_yearly_budget NUMBER EXECUTE g_yearly_budget := GET_BUDGET(11); VARIABLE g_yearly_budget NUMBER EXECUTE :g_yearly_budget := GET_BUDGET(11); VARIABLE :g_yearly_budget NUMBER EXECUTE :g_yearly_budget := GET_BUDGET(11); VARIABLE g_yearly_budget NUMBER :g_yearly_budget := GET_BUDGET(11); CREATE OR REPLACE PROCEDURE update_theater (v_name IN VARCHAR v_theater_id IN NUMBER) IS BEGIN UPDATE theater SET name = v_name WHERE id = v_theater_id; END update_theater; When invoking this procedure, you encounter the error: ORA-000: Unique constraint(SCOTT.THEATER_NAME_UK) violated.How should you modify the function to handle this error? Page 26 of 74
- 27. An user defined exception must be declared and associated with the error code and handled in the EXCEPTION section. Handle the error in EXCEPTION section by referencing the error code directly. Handle the error in the EXCEPTION section by referencing the UNIQUE_ERROR predefined exception. Check for success by checking the value of SQL%FOUND immediately after the UPDATE statement. Read the following code: CREATE OR REPLACE PROCEDURE calculate_budget IS v_budget studio.yearly_budget%TYPE; BEGIN v_budget := get_budget(11); IF v_budget < 30000 THEN set_budget(11,30000000); END IF; END; You are about to add an argument to CALCULATE_BUDGET. What effect will this have? The GET_BUDGET function will be marked invalid and must be recompiled before the next execution. The SET_BUDGET function will be marked invalid and must be recompiled before the next execution. Only the CALCULATE_BUDGET procedure needs to be recompiled. All three procedures are marked invalid and must be recompiled. Which procedure can be used to create a customized error message? RAISE_ERROR SQLERRM RAISE_APPLICATION_ERROR RAISE_SERVER_ERROR The CHECK_THEATER trigger of the THEATER table has been disabled. Which command can you issue to enable this trigger? ALTER TRIGGER check_theater ENABLE; ENABLE TRIGGER check_theater; ALTER TABLE check_theater ENABLE check_theater; ENABLE check_theater; Examine this database trigger CREATE OR REPLACE TRIGGER prevent_gross_modification {additional trigger information} BEGIN IF TO_CHAR(sysdate, DY) = MON THEN RAISE_APPLICATION_ERROR(-20000,Gross receipts cannot be deleted on Monday); END IF; END; This trigger must fire before each DELETE of the GROSS_RECEIPT table. It should fire only once for the entire DELETE statement. What additional information must you add? BEFORE DELETE ON gross_receipt AFTER DELETE ON gross_receipt BEFORE (gross_receipt DELETE) FOR EACH ROW DELETED FROM gross_receipt Examine this function: CREATE OR REPLACE FUNCTION set_budget (v_studio_id IN NUMBER, v_new_budget IN NUMBER) IS BEGIN UPDATE studio SET yearly_budget = v_new_budget WHERE id = v_studio_id; IF SQL%FOUND THEN Page 27 of 74
- 28. RETURN TRUEl; ELSE RETURN FALSE; END IF; COMMIT; END; Which code must be added to successfully compile this function? Add RETURN right before the IS keyword. Add RETURN number right before the IS keyword. Add RETURN boolean right after the IS keyword. Add RETURN boolean right before the IS keyword. Under which circumstance must you recompile the package body after recompiling the package specification? Altering the argument list of one of the package constructs Any change made to one of the package constructs Any SQL statement change made to one of the package constructs Removing a local variable from the DECLARE section of one of the package constructs Procedure and Functions are explicitly executed. This is different from a database trigger. When is a database trigger executed? When the transaction is committed During the data manipulation statement When an Oracle supplied package references the trigger During a data manipulation statement and when the transaction is committed Which Oracle supplied package can you use to output values and messages from database triggers, stored procedures and functions within SQL*Plus? DBMS_DISPLAY DBMS_OUTPUT DBMS_LIST DBMS_DESCRIBE What occurs if a procedure or function terminates with failure without being handled? Any DML statements issued by the construct are still pending and can be committed or rolled back. Any DML statements issued by the construct are committed Unless a GOTO statement is used to continue processing within the BEGIN section, the construct terminates. The construct rolls back any DML statements issued and returns the unhandled exception to the calling environment. Examine this code BEGIN theater_pck.v_total_seats_sold_overall := theater_pck.get_total_for_year; END; For this code to be successful, what must be true? Both the V_TOTAL_SEATS_SOLD_OVERALL variable and the GET_TOTAL_FOR_YEAR function must exist only in the body of the THEATER_PCK package. Only the GET_TOTAL_FOR_YEAR variable must exist in the specification of the THEATER_PCK package. Only the V_TOTAL_SEATS_SOLD_OVERALL variable must exist in the specification of the THEATER_PCK package. Both the V_TOTAL_SEATS_SOLD_OVERALL variable and the GET_TOTAL_FOR_YEAR function must exist in the specification of the THEATER_PCK package. A stored function must return a value based on conditions that are determined at runtime. Therefore, the SELECT statement cannot be hard-coded and must be created dynamically when the function is executed. Which Oracle supplied package will enable this feature? DBMS_DDL DBMS_DML DBMS_SYN DBMS_SQL Answers{ Thanks again for publishing my questions. Page 28 of 74
- 29. Tech Interviews comment by Sachin Rastogi (rsachin@krify.com) 1.1 2.2 3.1 4.(1,3,4) 5.2 6.3 7.4 8.2 9.2 10.(3,4) 11.1 12.4 13.1 14.1 15.3 16.3 17.1 18.(1,4) 19.4 20.3 21.4 22.2 23.4 24.3 25.4 please let me know how many answers are right. in this pl/sql test. Thanks & Regards, Sudhir Rao. Tech Interviews comment by Sudhir Answer to question-2 is 4 Tech Interviews comment by Unnamed 24 IS 4 Tech Interviews comment by dcz The answer to the question 8 is wrong; should be 3. Tech Interviews comment by Stephen Jacob Answer to number 9 should be 4. How can you check for the initial value, if there is no user input? Tech Interviews comment by Stephen Jacob The Answer to the question 8 is 3rd Choice. Tech Interviews comment by Ahamed Tharik.N Question 13 all the four answers are wrong , the function executed like this SQL> select get_budget(11) into :g_yearly_budget from dual; GET_BUDGET(11) ————– Let me know, if you have any Suggestions. Tech Interviews comment by Ahamed Tharik.N The Answer to the question 5 is 4rd Choice. If you are missing the END LOOP (2), the loop do not work, procedure does not compile. Tech Interviews comment by Francisco J. Banda The Answer to the question 5 is 1rd Choice. Page 29 of 74
- 30. Iti’s imposible that both 3 and 4 are correct. We do not need location (where) we need time (when). Tech Interviews comment by Francisco J. Banda The Answer to the question 5 is 3rd Choice. The 4rd (Oracle Forms trigger) is in some way correct, but oracle triggers and Forms triggers are not the same. This question is about Oracle triggers (not Forms). Tech Interviews comment by Francisco J. Banda Hi Ahamed Tharik.N your answer is correct, but also answer number 2 works to be able to see the result uses SQL>print g_yearly_budget. Tech Interviews comment by Francisco J. Banda The answer to the question 13 should be 2. I fully agree with Francisco J. Banda. For Francisco, your answers are right, just match question numbers. I tried to do and here is the revised answer list. (T means correct answer choice) 1.)1 : T 2.)2 - 4 : 4 - T 3.)1 : T 4.)(1,3,4) - T 5.)2 - 4 : 4 - T 6.)3 - T 7.)4 - T 8.)2 - 3 - 3 : 3 - T 9.)2 - 4 : 4 - T 10.)(3,4) - 1 11.)1 - [I dont know correct answer] 12.)4 - 3 : 3 - T 13.)1 - ? : 2 - T Thanks. Tech Interviews comment by Pranav Vora 1.1 2.4 3.2 4.1,3,5 5.2 6.2,3 7.1 8.3 9.4 10.4 11.4 12.1 13.2 14.4 15.3 16.2 17.2 18.1 19.4 20.3 21.4 22.2 23.4 24.4 25.4 Tech Interviews comment by Arti Shah The answer to the 23 is 4 Tech Interviews comment by vijay answer for 22 is 2 Page 30 of 74
- 31. Tech Interviews comment by vijay answer for 18 is 1 Tech Interviews comment by oraguru Right answer to QUS.5 is 4th option coz if end loop is missed in programming it wud through error while compiling , but if u missed EXIT , the program wud not know where to exit the loop …and loop wud go on Tech Interviews comment by cobra 1. 1 2. 4 3. 1 4. 1,3,4 5. 2 6. 2,3 7. 4 8. 3 9. 4 10. 1 11. 2 12. 3 13. 2 14.4 15. 3 16. 3 17.2 18. 1 19. 3 20.3 21. 4 22. 2 Tech Interviews comment by aa } Set 5 : SQL ,PL/SQL & D2K Interview Questions [message #27446] Fri, 03 October 2003 03:43 Gurusubramanyam Messages: 78 1. How to implement ISNUMERIC function in SQL *Plus ? Method 1: Select length (translate (trim (column_name),' +-.0123456789',' ')) from dual ; Will give you a zero if it is a number or greater than zero if not numeric (actually gives the count of non numeric characters) Method 2: select instr(translate('wwww', 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ', 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'),'X') FROM dual; It returns 0 if it is a number, 1 if it is not. 2. How to Select last N records from a Table? select * from (select rownum a, CLASS_CODE,CLASS_DESC from clm) where a > ( select (max(rownum)-10) from clm) Here N = 10 Page 31 of 74
- 32. The following query has a Problem of performance in the execution of the following query where the table ter.ter_master have 22231 records. So the results are obtained after hours. Cursor rem_master(brepno VARCHAR2) IS select a.* from ter.ter_master a where NOT a.repno in (select repno from ermast) and (brepno = 'ALL' or a.repno > brepno) Order by a.repno What are steps required tuning this query to improve its performance? ?Ï Have an index on TER_MASTER.REPNO and one on ERMAST.REPNO ?Ï Be sure to get familiar with EXPLAIN PLAN. This can help you determine the execution path that Oracle takes. If you are using Cost Based Optimizer mode, then be sure that your statistics on TER_MASTER are up-to-date. ?Ï Also, you can change your SQL to: SELECT a.* FROM ter.ter_master a WHERE NOT EXISTS (SELECT b.repno FROM ermast b WHERE a.repno=b.repno) AND (a.brepno = 'ALL' or a.repno > a.brepno) ORDER BY a.repno; 3. What is the difference between Truncate and Delete interms of Referential Integrity? DELETE removes one or more records in a table, checking referential Constraints (to see if there are dependent child records) and firing any DELETE triggers. In the order you are deleting (child first then parent) There will be no problems. TRUNCATE removes ALL records in a table. It does not execute any triggers. Also, it only checks for the existence (and status) of another foreign key Pointing to the table. If one exists and is enabled, then you will get The following error. This is true even if you do the child tables first. ORA-02266: unique/primary keys in table referenced by enabled foreign keys You should disable the foreign key constraints in the child tables before issuing the TRUNCATE command, then re-enable them afterwards. CLIENT/SERVER What does preemptive in preemptive multitasking mean ? Preemptive refers to the fact that each task is alloted fixed time slots and at the end of that time slot the next task is started. What does the OLTP stands for ? OLTP stands for On Line Transaction Processing What is the most important requirement for OLTP ? OLTP requires real time response. In a client server environment, what would be the major work that the client deals with ? The client deals with the user interface part of the system. Why is the most of the processing done at the sever ? To reduce the network traffic and for application sharing and implementing business rules. What does teh term upsizing refer to ? Page 32 of 74
- 33. Applications that have outgrown their environment are re-engineered to run in a larger environment. This is upsizing. What does one do when one is rightsizing ? With rightsizing, one would move applications to the most appropriate server platforms. What does the term downsizing refer to ? A host based application is re-engineered to run in smaller or LAN based environment. What is event trigger ? An event trigger, a segment of code which is associated with each event and is fired when the event occurs. Why do stored procedures reduce network traffic ? When a stored procedure is called, only the procedure call is sent to the server and not the statements that the procedure contains. What are the types of processes that a server runs ? Foreground process and Background process. What is a event handler ? An event handler is a routine that is written to respond to a particular event. What is an integrity constraint ? An integrity constraint allows the definition of certain restrictions, at the table level, on the data that is entered into a table. What are the various uses of database triggers ? Database triggers can be used to enforce business rules, to maintain derived values and perform value-based auditing. What is a transaction ? A transaction is a set of operations that begin when the first DML is issued and end when a commit or rollback is issued. BEGIN COMMIT/ROLLBACK are the boundries of a transaction. Why are the integrity constraints preferred to database triggers ? Because it is easier to define an integrity constraint than a database trigger. Why is it better to use an integrity constraint to validate data in a table than to use a stored procedure ? Because an integrity constraint is automatically checked while data is inserted into a table. A stored has to be specifically invoked. What are the three components of a client server model ? A Client, A Server and A Network/Communication software. What are the advantages of client/server model ? Flexibility of the system, scalability, cost saving, centralised control and implementation of business rules, increase of developers productivity, portability, improved network and resource utilization. What are the disadvantages of the client/server model ? Heterogeneity of the system results in reduced reliablity. May not be suitable for all applications. Managing and tuning networks becomes difficult. Page 33 of 74
- 34. What are the different topologies available for network ? Star, Bus, Ring. What is the first work of Client process ? A client process at first establishes connection with the Server. What are the responsibilities of a Server ? 1. Manage resources optimally across multiple clients. 2. Controlling database access and security. 3. Protecting the databse and recovering it from crashes. 4. Enforcing integrity rules globally. In a Client/Server context, what does API (Application Programming Interface) refer to ? An API, in a Client/Server context, is a specification of a set of functions for communication between the client and the server. Give some examples of standard API¡Šs ? Open Database Connectivity (ODBC), Integrated Database Application Programming Interface (IDAPI), XOpen SQL/CLI What is the main advantage of developing an application using an API ? The application can be connected to any back end server that is supported by the API. What is the main disadvantage of developing an application using an API ? The application cannot use any special features of the backend server. Why is an event driven program referred to a passive program ? Because an event driven program is always waiting for something to happen before processing. What are the four types of events ? 1. System Events. 2. Control Events 3. User Events 4. Other Events. What is the difference between file server and a database server ? A file server just transfers all the data requested by all its client and the client processes the data while a database server runs the query and sends only the query output. What is inheritance ? Inheritance is a method by which properties and methods of an existing object are automatically passed to any object derived from it. What are the two components of ODBC ? 1. An ODBC manager/administrator and 2. ODBC driver. What is the function of a ODBC manager ? Page 34 of 74
- 35. The ODBC Manager manages all the data sources that exists in the system. What is the function of a ODBC Driver ? The ODBC Driver allows the developer to talk to the back end database. What description of a data source is required for ODBC ? The name of the DBMS, the location of the source and the database dependent information. How is a connection establised by ODBC ? ODBC uses the description of the datasource available in the ODBC.INI file to load the required drivers to access that particular back end database. RDBMS FUNDAMENTALS I. INTRODUCING DATABASES : Concept of a Database : Traditional Approach : In this approach, independent application programs access their own independent data files. This results in many problems in data storage and retrieval. Database Approach : In this approach, all application access a common database, which is a centralized data storage system. This approach has the following advantages : Redundancy of data storage is reduced, Inconsistency in data is eliminated & Data sharing between applications is possible. Interacting with a Database : Database Management System (DBMS) : DBMS is a software that interfaces between applications and a database for all data processing activities. Users of a DBMS : End Users, Application Programmers and Database Administrators use a DBMS, either directly or indirectly. How users interact with a Database : 1. End users send queries to the DBMS through applications. 2. The DBMS translates the queries. 3. The DBMS retrieves data from the database. 4. The DBMS sends data to the application, which present the data to the end users. Functions of a DBMS : Function of DBMS Description Provided by using Defining the data structure Defining structure of data to be stored in database Data Definition Language (DDL) Manipulating Data Retrieving, adding, modifying, deleting data. Data Manipulation Language (DML) Data Security Preventing unauthorized access to data. User-ids and Passwords. Control of Data Access Allowing users to use only relevant data Data Control Language (DCL) Architecture of a Database : Need for an Architecture : The details about complexity and structure of data in a database in not required by end-users. Therefore, differentiating what the end-users see and what is actually there in a database is important. Architecture of a Database : The architecture of a database comprises a set of three levels at which a database can be viewed. External Level or View, Conceptual Level or View & Internal Level or View. II. USING RELATIONAL DATABASE : Basics of Relational Database : Relational Database Management System (RDBMS) : RDBMS is the most popular form of DBMS used in the world. It uses a relational database to organize data. A relational database comprise relations, which are represented as tables. Relation : A relation stores information about an object in the real world. A relation is represented as a table. Attribute : Each attribute of a relation stores a piece of information about an object. Attributes are represented as columns in a tables and can be arranged in any order. Each attribute in a relation is unique and contain atomic values i.e. Atomic value contain a single value of data and Non-Atomic values contain a set of values. The number of attributes in a relation is called the degree of the relation. Tuple : A row in a table is called a tuple of the relation. The number of tuples in a relation is known as the cardinality of the relation. Tuples in a table are unique and can be arranged in any order. Domain : A domain is a set of valid atomic values that an attribute can take. Within a single database, an attribute cannot have different domains associated with it. A domain can include a null value, if the value for the domain is unknown or does not exist. Identifiers for Relations : Primary Key : An attribute that uniquely identifies a row in a table is called its primary key. A relation can have only one primary key. The primary key cannot have any null values. In case no unique key is found in a relation, two or more attributes can be treated as the primary key. Such keys are called Composite Keys. Page 35 of 74
- 36. Candidate Key : A relation can have more than one attribute that uniquely identifies a tuple. Any one of these keys can be selected as the primary key. All such attributes are called Candidate Keys. All candidate keys that are not primary keys are called Alternate Keys. Foreign Key : An attribute that is not a candidate key is called a Nonkey. A nonkey attribute of a relation whose value matches the primary key in some other table is called Foreign Key OR is a column in a table that uniquely identifies rows from a different table. III. INTERPRETING DATA : Entities and Relationships : Entity : An entity is an object that exists in the real world and is distinguishable from other objects. Each entity is represented as a table in a relational database. Types of Entities : Entities can be classified in two ways - based on existence and based on subsets. Based on existence, entities can be classified as Dominant and Weak entities. Based on subsets, entities can be classifies as Supertypes and Subtypes. Relationships : A relationship is an association between two entities. Types of Relationships : Relationships are classified into three types based on the occurrence of the related entities. One-to-One(1-1), One-to-Many(1-M) & Many-to-Many(M-M). Using E/R Diagram : A E/R diagram represent entities and relationships in a database system. Reducing E/R Diagrams to Relations : Mapping Entities : A dominant entity is mapped to a new relation. A weak entity is mapped to a new relation. The primary key of the corresponding dominant entity is included as the foreign key in the weak entity relation. Supertypes and subtypes are mapped to separate relations. The primary key of the supertype becomes the primary key of the subtype. Mapping Relationships : A 1-1 relationship is mapped using a foreign key. The primary key of either of the entities is include as a foreign key in the relation of the other entity. This relationship is rare, because data elements related in this way are normally placed in the same table. A 1-M or M-1 is mapped by introducing a foreign key. A primary key is the ¡¥one¡Š side of the relationship, and the foreign key is the ¡¥many¡Š side of the relationship. This relationship are most common. A M-M involves the creation of a new relation. M-M are problematic and cannot be adequately expressed directly in a relational db. It is expressed using intersection tables. An intersection table contains two (or more) foreign keys, relating the primary key values of two (or more) tables to each other. The role of an intersection table is to convert the M-M into two 1-M relationships that can be easily handled by the database. IV. SIMPLIFYING DATA : Need for Simplifying Data : Normalization : Normalization is a formal process of developing data structures in a manner that eliminates redundancy and promotes integrity. You need to simplify structure of data in relations for easy storage and retrieval. The process of simplifying relations is called normalization. The new relations that are obtained after normalization are called normalized relations. Normalization has three well defined steps : The relations that you get at the end of the first step are said to be in 1NF. The relations that you get at the end of the second step are said to be in 2NF. The relations that you get at the end of the third step are said to be in 3NF. Simplifying Data to 1NF (Eliminate Repeating Groups) : A repeating group is a set of columns that store similar info that repeats in the same table. To simplify data to 1NF, you ensure that all attributes values in a relation have atomic values. If there are attributes in a relation with non-atomic values, move these attributes to a new relation and choose an appropriate primary key for it. E.g. SupItem Table Item field having atomic. Simplifying Data to 2NF (Eliminate Redundant Data) : Redundant data is data that is expressed multiple times unnecessarily, or depends only on part of a multi-valued key. Functionally Dependent Attributes : Functionally Dependent Attributes are those that belong to a single entity or relationship and depend on its unique identifier. To simplify data to 2NF, you ensure that all nonkey attributes in a relation are functionally dependent on the whole key and not part of the key. Conversion from 1NF to 2NF : To convert a relation in 1NF to 2NF, move all nonkey attributes that are not wholly dependent on the primary key, to a new relation. Then, choose an appropriate primary key for the new relation. E.g. Separating Sup. table and Item table. Simplifying Data to 3NF (Eliminate Columns not Dependent on the Key) : Columns in each table should be a group of columns in which the data in each column contributes to the description of each row in the table. Transitively Dependent Attributes : Transitively Dependent Attributes in a relation are those that are dependent on a nonkey attribute and not the primary key. To simplify data to 3NF, you ensure that there are no attributes in a relation that are transitively dependent on other attributes. Conversion from 2NF to 3NF : To convert a relation in 2NF to 3NF, move all transitively dependent attributes to a new relation. Then, choose an appropriate primary key for the new relation. E.g. Status is dependent on City in Sup. table, so move those two to separate table. Simplifying Data to 4NF (Isolate Independent Multiple Relationships) : V. STORING & RETRIEVING DATA : Language Support for an RDBMS : Page 36 of 74
- 37. SQL :SQL is the language that provides command to interact with the data in the database. SQL consists of three components - DDL, DML & DCL. DDL : DDL comprises commands you can use to create and modify the database structure. DML : DML comprises commands you can use to add, modify, delete and query data in the database. DCL : DCL comprises commands you can use to control the user access to the database. Organizing the Database : Base Tables : A database comprises base tables, which have the following features : They physically exist on the disk, Each of them has a unique name & they contain data that is crucial to an organization. Their attributes have data types such as character, integer, decimal, date and time. CREATE TABLE : This is a DDL command in SQL that creates a new table in a database. Syntax : CREATE TABLE table-name (column-name data-type [[size]] NOT NULL/DEFAULT default-value]] CHECK (column-name > 0) UNIQUE (column-name) PRIMARY KEY (column-name) FOREIGN KEY (column-name) REFERENCES table-name) ALTER TABLE : This is a DDL command in SQL that modifies the structure of an existing table. Syntax : ALTER TABLE table-name ADD (column-name data-type [[size]] [[NOT NULL DEFAULT]]...) primary key definition / foreign key definition DROP PRIMARY KEY / DROP FOREIGN KEY) DROP TABLE : This is DDL command in SQL that deletes the an existing table. Once you delete a table, all data contained in it is lost and cannot be recovered. The storage space used by this table is also released. Syntax : DROP TABLE table-name Interacting with a Database : SELECT : This is a DML command in SQL that retrieves data from the database in the form of query results. The command supports the following keywords and clauses : FROM This keyword specifies the name of the table. * This keyword selects all the columns of the table. WHERE This keyword gives the search condition that specifies the data to be retrieved. AND This operator is used to combine two or more search conditions. ORDER BY This keyword sorts the query result on one or more columns. GROUP BY This keyword groups the query result and lets you generate summary result for each group. NULL values This value indicates that the data is not present. Subquery This is the query that is place inside the main query. It passes its query result to the main query. INSERT : This is a DML command in SQL that you use to add data in rows of a table. SYNTAX : INSERT INTO table-name (column-names) VALUES (constant/NULL) UPDATE : This is a DML command in SQL that you use to change data on rows of a table. Syntax : UPDATE table-name SET column-name-value WHERE condition DELETE : This is a DML command in SQL that removes one or more rows of data from a table. Syntax : DELETE FROM table-name WHERE condition. End-user's View of a Database : Views : Views are relations that are derived from one or more source tables. Views have the following features: Views let you restrict the access to data so that end-users see data relevant to them. Views do not physically exist in the database and only their definition is stored by an RDBMS. An RDBMS accesses the source tables for data to be retrieved from a view. Any changes that users make to views do not reflect in the source tables if the view has been created using a Join condition. Views created WITH CHECK OPTION allows for an added measure of security in a view. For example, the user will not be able to insert or update a row that could not be selected by the view-with check option prevents this from happening. CREATE VIEW : A view can be created using the CREATE VIEW command. Syntax : CREATE VIEW view-name (column-names) AS query. Retrieving Data from a View : Once you create a view, you can retrieve data from it using the SELECT command, just as you do for a table. Restricting Access to a Database : GRANT : This is a DCL command in SQL that you use to grant a specific set of authorities to one or more users. Syntax : GRANT (SQL command) (column-names) ON table-name TO user-name. REVOKE : This is a DCL command in SQL that you use to take away a specific set of authorities from one or more users. Syntax : REVOKE (SQL command) ON table-name TO user-name. VI. ENSURING INTEGRITY OF DATA : The concept of Data Integrity : Data Integrity : Data Integrity refers to the correctness and completeness of data in a database. Integrity Constraints : Integrity constraints allows only correct changes to be made to a database. There are two types of integrity constraints - entity integrity and referential integrity. Page 37 of 74
- 38. Entity Integrity : Entity Integrity ensures that for each row in a table, the value of the primary key is unique and is not null. Referential Integrity : Referential Integrity ensures that for each row in a table, the value of the foreign key is present in the reference table. Grouping commands related to a task : Transaction Processing : A transaction is a sequence of one or more SQL commands that together form a logical task. Transaction Processing ensures that when the RDBMS is making changes related to a single task, either all changes are made as a unit or no changes are made. Commit : Commit is an SQL command that indicates the successful end of a transaction. After an RDBMS executes this command all the changes are made to the database. Rollback : Rollback is an SQL command that cancels a transaction before it is complete. The rollback command removes the changes of all previous commands in a transaction from the buffer. Controlling Concurrent Data Access : Concurrency Control : All RDBMS must ensure that the transactions of concurrent users do not interfere with each other. If it does not handle the transactions properly, the problems of lost update, uncommitted data, or inconsistent data might occur. Lost Update Problem : Lost update problem occurs when an update made by a transaction is lost due to an update made by another transaction. Uncommitted Data Problem : Uncommitted data problem occurs when a transaction accesses data that has been updated by a previous transaction that has not yet ended. Inconsistent Data Problem : Inconsistent data problem occurs when a transaction accesses data from the database and simultaneously another transaction is changing that data. Locking : Locking is a facility provided by an RDBMS to ensure that a transaction does not interfere with any other transaction. Locking prevents the problem of lost update, uncommitted data and inconsistent data. An RDBMS provided two types of locks for locking a part of the database - shared locks and exclusive locks. Shared Locks : If a transaction is only reading data from a database, it gets a shared lock on that part of the database. Other transactions can also get a shared lock on that part of the database to read data. However, they cannot change the data. Exclusive Locks : If a transaction is updating data in a database, it gets an exclusive lock on that part of the database. No other transaction can read or change this data. Client Server Computing Model I. Client Server Paradigm : Introduction : In the past decade, organizations have restructured and become global. The globalization and restructuring have led to a need for distributed and flexible information access. That traditional computing paradigms like host-based and master/slave processing do not adequately address the information requirements of modern business. That the client/server model provides an architecture that harness contemporary technology to meet the computing needs of the modern business organization. Also called Distributed Application Processing or Co-Operative Application Processing Host Based Processing - The Centralized Paradigm : Centralized computing treated applications as an integrated unit. Applications ran on a single processor. The same processor generated the user interface and manipulated data. Dumb terminals were used for data access and display. Disadvantages are : Data was centralized and often not accessible to those who needed it. The host computed did all the work, was frequently overloaded, and response times were often poor. Hardware choices and scalability were limited by proprietary architecture's. User interfaces were unfriendly, Data access was inflexible and governed by available 3GL programs. Master/Slave - The First Distributed Computing Paradigm : As PC's and intelligent terminals became available, a limited amount of processing was transferred to the terminal. Intelligent terminals often validated data and provided editing functions. Such terminal were called Slaves. Slaves were controlled by Master computer which did the main processing and stored all data. It had one distinct advantage. It reduced the load on the main processor. However, the other problems associated with host-based processing remained. Client/Server - A Distributed Computing Paradigm : The client/server paradigm evolved as an attempt to address the new computing needs of business and utilize new technologies. Advantages : Client/Server makes it possible to harness the computing power available on PCs and other workstations in an organization. Response times are improved as processors are not overloaded. Hardware and software choices can be application oriented as they do not necessarily have to run on a proprietary computer. Network traffic is reduced because the processing power available at the end user terminal makes it unnecessary to send detailed instructions over the network as in the case of host based & master/slave systems. Computing power can be added in smaller units making the system easily scaleable. Disadvantages :The inherent heterogeneity makes System Integration, Administration & Maintenance a formidable challenge. ORACLE 7 is an exceptional RDBMS & also an excellent DB server because it supports all major OS for both clients & servers i.e. MSDOS, Netware, Unixware, OS/2 etc. Oracle Network software SQL*NET support all major network communication protocols TCP/IP, SPX/IPS, Named Pipes & DECNET. It has got client server feature that developers can use to minimize network traffic between clients & servers. Has features that makes it easy to administer a complicated client server system. Page 38 of 74
- 39. Client/Server Approach : The client/server paradigm optimizes the use of computer resources by distributing application processing among multiple processors. The client/server model computers are classified as Clients and Servers, where Clients are requesters of services and Servers are provider of services. Typically, clients handle user interface function & server handle data management function. Client/Server Architecture requires Processing to be distributed over more than one computing system. Client-initiated client/server interactions. Server control over the services that can be requested by the client. Servers to arbitrate between conflicting client requests. A communication system that enables clients & servers to communicate. Multitasking can be defines as the capability of an OS to run multiple applications concurrently. A Multitasking OS allocates a certain amount of CPU time to each task. In Preemptive multitasking, the OS controls the amount of CPU time allocated to a task. In non-preemptive multitasking, the application controls the CPU time and the CPU is released only after the task is completed. Multithreading is an extension of multitasking. It allows multitasking within an application. Programs and subroutines within a program can execute concurrently in a multithreaded environment. Several user process for a single server process. Database Server should have preemptive multitasking & multithreading capability. Support a standard RDBMS. Support a standard Network Operating System. Tools such as RDBMS, Application Software, Application Program Interfaces, Stored Procedures, Remote Procedure Call (RPC) & Application Development Tools are an important part of client/server systems. Such tools improve productivity and also play a role in making client/server systems more open. An API is a set of functions that translates client requests into a format that the server can understand. RPC is essentially a messaging system which allows stored procedures to be invoked. Many RPCs allows procedures to be invoked across heterogeneous platforms and also provide the required data translation services. There are several application designs possible in the client/server model depending on how application processing is distributed. In Distributed Presentation, the presentation function is divided between the client & the server. Useful in situations where PC or workstations are connected to mainframes. Used to enhance the user interface of mainframe based applications. In Remote Presentation, the entire presentation part of the application resides on a different computer than the one that has the logic function. Used in applications where user interaction is completely static and predetermined. In Distributed Logic, the logic function is placed on more than one platform thus, improving response time by allowing the logic to execute simultaneously on several processors. In Remote Data Management, the application logic resides on different computer than the one that has the data and the DBMS. Easy to implement and often provide end-users with totally transparent access to data. In Distributed Data Management, the data and DBMS is distributed among multiple nodes and distribution of application logic. Goals of Client/Server Paradigm is the end-user. Client/Server seeks to provide end-user transparent access to the computing resources of the organization. The goal is referred to as single system image. There are four attributes of single system image : Location Transparency : Users must be able to access data without knowing the location of the data. Users should not have to learn & use different commands for accessing data from different locations. Interoperability requires that applications and processing tasks be freely portable across heterogeneous computing resources. Consistent User Interfaces require that applications retain the same user interface across heterogeneous computing platforms. Common computing tasks are represented consistently across applications. Enterprise-wide Resource Sharing is the common thread that links all of an enterprise's computing resource II. Concepts for Client/Server : Introduction : RDBMS's standardize data storage and access and are therefore ideal for implementing client/server systems. The physical structure of a network is called Network Topology i.e. refers to the way the cabling of a network is physically structured. The rules that govern the process of data transmission in a network are collectively referred to as Network Protocol. Graphical User Interfaces improve productivity because they reduce learning time and are easier to use. Distributed Database Support : The capability of an RDBMS to manage databases lying at more than one location. To provide distributed database support, an RDBMS must be able to provide transparent access to data, Join tables on different platforms, Handle and manage distributed queries and Ensure that transactions are successfully completed on all relevant databases. Network : Network has six basic functions, Naming, Segmentation, Segmenting, Flow Control, Synchronization, Priority & Error Control. There are three types of network topologies, Bus, Star & Ring. There are three types of transmission media, Twisted Pair, Coaxial Cable & Optic Fibre. There are three types of data transmission methods, Centralized, Distributed & Random. GUIs : GUI must support mouse events, keyboard events, menu events, resizing events, activation/deactivation events and initialize/terminate events. GUI should be portable, should support wide variety of development tools & be an industry standard. III. Client/Server Software : Back-end Software : It is made up of Database Servers & Network Operating Systems. The database server manages data on the system & maintains data integrity. Database server requires some special features. Compatibility i.e. must be able to work on different operating systems. SQL Implementation i.e. must support standard ANSI SQL since it can Page 39 of 74
- 40. communicate with different SQL dialects. Stored Procedures i.e. must be able to use SP as they are analyzed, compiled and optimized. Referential Integrity i.e. allows the server to synchronize change to columns that are part of multiple tables. Declarative RI establishes precise rules for use of columns that are common across tables. Built into db software and enforced by default. In Procedural RI, each db command is associated with a trigger. When command is issued, the trigger sets of a series of commands that make the necessary changes. Disadvantage is programmers must write triggers leading to errors. Multithreading i.e. support execution of multiple tasks simultaneously. Distributed Database Support i.e. able to divide database tasks among multiple CPUs. Also, able to join tables located on different servers, & manage SQL queries sent to different servers. Concurrency Control i.e. support automatic escalation, the server locks a record, if a single record is being modified. A page, if several records are being modified. A table, if several pages are being modified. Transaction Control i.e. protect transactions from system failures. In two phase commit, all workstations are notified of database changes, and if system fails, all sites rollback. NOS controls the transmission of data across the network and manages the sharing of hardware and software resource on the network. Four important features are Operating Environment Support, Workstation Support, Security & Protocol Support. Development Tools are made up of SQL/3GL programming tools & Front-end development tools. End User Tools are made up of Decision Support Tools and PC-based add-ons. IV. Migrating to Client/Server : Evaluating the Client/Server Option : To evaluate the following before deciding on client/server. Application requirements, Geographical requirements & Productivity Gains. Client/Server is most suitable for applications are decision support or on-line transaction processing (OLTP). The distances are site or city & both developer & end-user productivity are expected to increase. Planning for Migration : Planning is needed to reduce problems with network load, training & systems maintenance. Migration plan must include analysis, selection, prototyping & implementation as activities. Planning must include end- users, developers and system administrators as resources. To specify system requirements for end-users, developers, system managers and the business as a whole. To evaluate business priorities to eliminate stagnation & disruption. Implementing Client/Server : The Systems Integration Life Cycle (SILC) is made up of preparation, detailing and execution. Managing SILC projects involves planning, controlling & completing. System maintenance involves ensures reliability, ensuring serviceability and monitoring performance. The training must cover end-users, developers & system administrators. ORACLE I. SQL*PLUS : SQL is an English like language consisting of commands to store, retrieve, maintain & regulate access to your database. SQL*PLUS is an application that recognizes & executes SQL commands & specialized SQL*Plus commands that can customize reports, provide help & edit facility & maintain system variables. NVL : Null value function converts a null value to a non-null value for the purpose of evaluating an expression. Numeric Functions accept numeric I/P & return numeric values. They are MOD, SQRT, ROUND, TRUNC & POWER. Date Functions are ADD_MONTHS, LAST_DAY, NEXT_DAY, MONTHS_BETWEEN & SYSDATE. Character Functions are INITCAP, UPPER, LOWER, SUBSTR & LENGTH. Additional functions are GREATEST & LEAST. Group Functions returns results based upon groups of rows rather than one result per row, use group functions. They are AVG, COUNT, MAX, MIN & SUM. TTITLE & BTITLE are commands to control report headings & footers. COLUMN command define column headings & format data values. BREAK command clarify reports by suppressing repeated values, skipping lines & allowing for controlled break points. COMPUTE command control computations on subsets created by the BREAK command. SET command changes the system variables affecting the report environment. SPOOL command creates a print file of the report. JOIN is the form of SELECT command that combines info from two or more tables. Types of Joins are Simple (Equijoin & Non-Equijoin), Outer & Self join. Equijoin returns rows from two or more tables joined together based upon a equality condition in the WHERE clause. Non-Equijoin returns rows from two or more tables based upon a relationship other than the equality condition in the WHERE clause. Outer Join combines two or more tables returning those rows from one table that have no direct match in the other table. Self Join joins a table to itself as though it were two separate tables. Set Operators supported by Oracle are : Union is the product of two or more tables. Intersect is the product of two tables listing only the matching rows. Minus is the product of two tables listing only the non-matching rows. Correlated Subquery is a subquery that is evaluated once for each row processed by the parent statement. Parent statement can be Select, Update or Delete. Use CRSQ to answer multipart questions whose answer depends on the value in each row processed by parent statement. Multiple columns can be returned from a Nested Subquery. Sequences are used for generating sequence numbers without any overhead of locking. Drawback is that after generating a sequence number if the transaction is rolled back, then that sequence number is lost. Page 40 of 74
- 41. Synonyms is the alias name for table, views, sequences & procedures and are created for reasons of Security and Convenience. Two levels are Public - created by DBA & accessible to all the users. Private - Accessible to creator only. Advantages are referencing without specifying the owner and Flexibility to customize a more meaningful naming convention. Indexes are optional structures associated with tables used to speed query execution and/or guarantee uniqueness. Create an index if there are frequent retrieval of fewer than 10-15% of the rows in a large table and columns are referenced frequently in the WHERE clause. Implied tradeoff is query speed vs. update speed. Oracle automatically update indexes. Concatenated index max. is 16 columns. Data types : Max. columns in a table is 255. Max. Char size is 255, Long is 64K & Number is 38 digits. Cannot Query on a long column. Char, Varchar2 Max. size is 2000 & default is 1 byte. Number(p,s) p is precision range 1 to 38, s is scale -84 to 127. Long Character data of variable length upto 2GB. Date Range from Jan 4712 BC to Dec 4712 AD. Raw Stores Binary data (Graphics Image & Digitized Sound). Max. is 255 bytes. Mslabel Binary format of an OS label. Used primarily with Trusted Oracle. Order of SQL statement execution : Where clause, Group By clause, Having clause, Order By clause & Select. Transaction is defined as all changes made to the database between successive commits. Commit is an event that attempts to make data in the database identical to the data in the form. It involves writing or posting data to the database and committing data to the database. Forms check the validity of the data in fields and records during a commit. Validity check are uniqueness, consistency and db restrictions. Posting is an event that writes Inserts, Updates & Deletes in the forms to the database but not committing these transactions to the database. Rollback causes work in the current transaction to be undone. Savepoint is a point within a particular transaction to which you may rollback without rolling back the entire transaction. Set Transaction is to establish properties for the current transaction. Locking are mechanisms intended to prevent destructive interaction between users accessing data. Locks are used to achieve Consistency : Assures users that the data they are changing or viewing is not changed until the are thro' with it. Integrity : Assures database data and structures reflects all changes made to them in the correct sequence. Locks ensure data integrity and maximum concurrent access to data. Commit statement releases all locks. Types of locks are given below. Data Locks protects data i.e. Table or Row lock. Dictionary Locks protects the structure of database object i.e. ensures table's structure does not change for the duration of the transaction. Internal Locks & Latches protects the internal database structures. They are automatic. Exclusive Lock allows queries on locked table but no other activity is allowed. Share Lock allows concurrent queries but prohibits updates to the locked tables. Row Share allows concurrent access to the locked table but prohibits for a exclusive table lock. Row Exclusive same as Row Share but prohibits locking in shared mode. Shared Row Exclusive locks the whole table and allows users to look at rows in the table but prohibit others from locking the table in share or updating them. Share Update are synonymous with Row Share. Deadlock is a unique situation in a multi user system that causes two or more users to wait indefinitely for a locked resource. First user needs a resource locked by the second user and the second user needs a resource locked by the first user. To avoid dead locks, avoid using exclusive table lock and if using, use it in the same sequence and use Commit frequently to release locks. Mutating Table is a table that is currently being modified by an Insert, Update or Delete statement. Constraining Table is a table that a triggering statement might need to read either directly for a SQL statement or indirectly for a declarative Referential Integrity constraints. Pseudo Columns behaves like a column in a table but are not actually stored in the table. E.g. Currval, Nextval, Rowid, Rownum, Level etc. SQL*Loader is a product for moving data in external files into tables in an Oracle database. To load data from external files into an Oracle database, two types of input must be provided to SQL*Loader : the data itself and the control file. The control file describes the data to be loaded. It describes the Names and format of the data files, Specifications for loading data and the Data to be loaded (optional). Invoking the loader sqlload username/password controlfilename <options> PL/SQL : Data types are NUMBER, CHAR/VARCHAR2, DATE & BOOLEAN. Arrays are not allowed & only one identifier per line is allowed. Attributes of PL/SQL objects are %TYPE, %ROWTYPE. PL/SQL Block is a standard PL/SQL code segment. Block consists of three parts. Declarative Section for variables, constants & exceptions. This section is optional. Executable Section which is mandatory. Page 41 of 74
- 42. Exception Handlers which is optional. PL/SQL supports only DML i.e. INSERT, UPDATE, DELETE & SELECT...INTO. SQL Functions can be referenced within a SQL statement i.e. Numeric (SQRT,ROUND,POWER), Character (LENGTH,UPPER), DATE (ADD_MONTHS,MONTHS_BETWEEN) & Group (AVG,MAX,COUNT). Most SQL functions are available outside SQL statement except for group functions. Code Simple Loops repeats a sequence of statements multiple times. Syntax : LOOP <Sequence of Statements> END LOOP; Code Numeric FOR Loops repeat a sequence of statements a fixed number of times. Syntax : FOR <index> IN [[ REVERSE ]] <integer>..<integer> LOOP <sequence of statements> END LOOP; <index> is implicitly of type number. Defined only within the loop & Value can be referenced in an expression, but a new value cannot be assigned to the index within the loop. Code While Loops repeats a sequence of statements until a specific condition is no longer TRUE. Syntax : WHILE <condition> LOOP <sequence of statements> END LOOP; <condition> can be any legal PL/SQL condition & statements will be repeated as long as condition evaluates to TRUE. Code GOTO Statements jumps to a different place in the PL/SQL block. Syntax : GOTO label_name; Legally use a GOTO a statement that is in the same sequence of statements as the GOTO. In the sequence of statements that encloses the GOTO statement (outer block). Labels can label any statement. Used as targets for GOTO statements, use labels for blocks and loops, Label a block to allow referencing of DECLAREd objects that would otherwise not be visible because of scoping rules, Label a block to allow a variable to be referenced that might be hidden by a column name, Label a loop to allow an object to be reference that would otherwise not be visible because of scoping rules & Label an EXIT as a convenient way to specify exits from outer loops. Cursors are associated with every SQL DML statement processed by PL/SQL. Two types are Explicit i.e. Multiple row SELECT statements & Implicit i.e. INSERT, UPDATE, DELETE & SELECT...INTO statements. Implicit cursor is called the SQL cursor-it stores info concerning the processing of the last SQL statement not associated with an explicit cursor. OPEN, FETCH & CLOSE do not apply. All cursor attributes apply. Cursor has to be explicitly defined when a query returns multiple rows to process beyond the first row returned by the query & to keep track of which row is currently being processed. Declare the cursor to associate its name with a SELECT statement. Syntax : DECLARE CURSOR <cursor_name> IS <regular_select_statement>; Open the cursor to process the SELECT statement and store the returned rows in the cursor. Syntax : OPEN <cursor_name>; Fetch data from the cursor and store it in specified variables. Syntax : FETCH <cursor_name> INTO <var1, var2...>; Close the cursor to free up resources. Cursors must be closed before they can be reopened. Syntax : CLOSE <cursor_name> Explicit Cursor Attributes are %NOTFOUND, %FOUND, %ROWCOUNT & %ISOPEN. Reference the current cursor row with the WHERE CURRENT OF statement. The cursor must be declared with a FOR UPDATE OF clause. Syntax : WHERE CURRENT OF <cursor_name> Reference Cursors FOR Loops to specify a sequence of statements to be repeated once for each row that is returned by the cursor with the Cursor FOR Loop. Syntax : FOR <record_name> IN <cursor_name> LOOP --statements to be repeated go here END LOOP; Cursor FOR loops (CFL) are similar to Numeric For Loops(NFL). CFL specify a set of rows from a table using the cursor's name. NFL specify an integer range. CFL record takes on vales of each row. NFL index takes on each value in the range. Record_name is implicitly declared as record_name cursor_name%ROWTYPE When a CFL is initiated, an implicit OPEN cursor_name is initiated. For each row that satisfies the query associated with the cursor, an implicit FETCH is executed into the components of record_name. When there are no more rows left to FETCH, an implicit CLOSE cursor_name is executed and the loop is exited. Declare cursors to use parameters Syntax : DECLARE CURSOR <cursor_name> [[(param_name param_type)]] IS <regular select statement>; Page 42 of 74
- 43. Exception Handlers : In PL/SQL, errors are called exceptions. When an exception is raised, processing jumps to the exception handlers. An exception handler is a sequence of statements to be processed when a certain exception occurs. When an exception handler is complete, processing of the block terminates. Two types are Predefined Internal Exceptions which corresponds to approximately 20 common ORACLE errors & Raised automatically by PL/SQL in response to an ORACLE error. Eg.too_many_rows,no_data_found,invalid_cursor,value_errori.e. arithmetic,numeric,string,conversion or constraint error occurred, zero_divide, dup_val_on_index,cursor_already_open etc. User-Defined Exceptions must be declared & must be RAISEd explicitly. Only one handler per block may be active at a time & If an exception is raised in a handler, the search for a handler for the new exception begins in the enclosing block of the current block. Exception-Init : Exceptions may only be handled by name not ORACLE error number. So, name an ORACLE error so that a handler can be provided specifically for that error. Syntax : PRAGMA EXCEPTION_INIT (<user_defined_exception_name>, <ORACLE_error_number>); SQLCODE & SQLERRM provides info on the exception currently being handled & especially useful in the OTHERS handler. SQLCODE returns the ORACLE error number of the exception, or 1 if it was a user-defined exception. SQLERRM returns the ORACLE error message associated with the current value of SQLCODE & can also use any ORACLE error number as an argument. SQLCODE & SQLERRM cannot be used within a SQL statement. If no exception is active SQLCODE = 0 & SQLERRM = 'normal, successful completion'. Oracle : 1) What are the Back ground processes in Oracle and what are they. This is one of the most frequently asked question.There are basically 9 Processes but in a general system we need to mention the first five background processes.They do the house keeping activities for the Oracle and are common in any system. The various background processes in oracle are a) Data Base Writer(DBWR) : Data Base Writer Writes Modified blocks from Database buffer cache to Data Files.This is required since the data is not written whenever a transaction is commited. b) LogWriter(LGWR) : LogWriter writes the redo log entries to disk. Redo Log data is generated in redo log buffer of SGA. As transaction commits and log buffer fills, LGWR writes log entries into a online redo log file. c) System Monitor(SMON) : The System Monitor performs instance recovery at instance startup.This is useful for recovery from system failure d) Process Monitor(PMON) : The Process Monitor peforms process recovery when user Process fails. Pmon Clears and Frees resources that process was using. e) CheckPoint(CKPT) : At Specified times, all modified database buffers in SGA are written to data files by DBWR at Checkpoints and Updating all data files and control files of database to indicate the most recent checkpoint f) Archieves(ARCH) : The Archiver copies online redo log files to archival storal when they are busy. g) Recoveror(RECO) : The Recoveror is used to resolve the distributed transaction in network h) Dispatcher (Dnnn) : The Dispatcher is useful in Multi Threaded Architecture i) Lckn : We can have upto 10 lock processes for inter instance locking in parallel sql. 2) How many types of Sql Statements are there in Oracle There are basically 6 types of sql statments.They are a) Data Defination Language(DDL) : The DDL statments define and maintain objects and drop objects. b) Data Manipulation Language(DML) : The DML statments manipulate database data. c) Transaction Control Statements : Manage change by DML d) Session Control : Used to control the properties of current session enabling and disabling roles and changing .e.g Alter Statements,Set Role e) System Control Statements : Change Properties of Oracle Instance .e.g:: Alter System f) Embedded Sql : Incorporate DDL,DML and T.C.S in Programming Language.e.g:: Using the Sql Statements in languages such as 'C', Open,Fetch, execute and close 3) What is a Transaction in Oracle A transaction is a Logical unit of work that compromises one or more SQL Statements executed by a single User. According to ANSI, a transaction begins with first executable statment and ends when it is explicitly commited or rolled back. 4) Key Words Used in Oracle The Key words that are used in Oracle are a) Commiting : A transaction is said to be commited when the transaction makes permanent changes resulting from the SQL statements. b) Rollback : A transaction that retracts any of the changes resulting from SQL statements in Transaction. c) SavePoint : For long transactions that contain many SQL statements, intermediate Page 43 of 74
- 44. markers or savepoints are declared. Savepoints can be used to divide a transactino into smaller points. d) Rolling Forward : Process of applying redo log during recovery is called rolling forward. e) Cursor : A cursor is a handle ( name or a pointer) for the memory associated with a specific stament. A cursor is basically an area allocated by Oracle for executing the Sql Statement. Oracle uses an implicit cursor statement for Single row query and Uses Explcit cursor for a multi row query. f) System Global Area(SGA) : The SGA is a shared memory region allocated by the Oracle that contains Data and control information for one Oracle Instance.It consists of Database Buffer Cache and Redo log Buffer. g) Program Global Area (PGA) : The PGA is a memory buffer that contains data and control information for server process. h) Database Buffer Cache : Databese Buffer of SGA stores the most recently used blocks of datatbase data.The set of database buffers in an instance is called Database Buffer Cache. i) Redo log Buffer : Redo log Buffer of SGA stores all the redo log entries. j) Redo Log Files : Redo log files are set of files that protect altered database data in memory that has not been written to Data Files. They are basically used for backup when a database crashes. k) Process : A Process is a 'thread of control' or mechansim in Operating System that executes series of steps. 5) What are Procedure,functions and Packages Procedures and functions consist of set of PL/SQL statements that are grouped together as a unit to solve a specific problem or perform set of related tasks. Procedures do not Return values while Functions return one One Value Packages Provide a method of encapsulating and storing related procedures, functions, variables and other Package Contents 6) What are Database Triggers and Stored Procedures Database Triggers :: Database Triggers are Procedures that are automatically executed as a result of insert in, update to, or delete from table. Database triggers have the values old and new to denote the old value in the table before it is deleted and the new indicated the new value that will be used. DT are useful for implementing complex business rules which cannot be enforced using the integrity rules.We can have the trigger as Before trigger or After Trigger and at Statement or Row level. eg. operations insert,update ,delete 3 before ,after 3*2 A total of 6 combinatons At statment level(once for the trigger) or row level( for every execution ) 6 * 2 A total of 12. Thus a total of 12 combinations are there and the restriction of usage of 12 triggers has been lifted from Oracle 7.3 Onwards. Stored Procedures : Stored Procedures are Procedures that are stored in Compiled form in the database.The advantage of using the stored procedures is that many users can use the same procedure in compiled and ready to use format. 7) How many Integrity Rules are there and what are they There are Three Integrity Rules. They are as follows :: a) Entity Integrity Rule : The Entity Integrity Rule enforces that the Primary key cannot be Null b) Foreign Key Integrity Rule : The FKIR denotes that the relationship between the foreign key and the primary key has to be enforced.When there is data in Child Tables the Master tables cannot be deleted. c) Business Integrity Rules : The Third Intigrity rule is about the complex business processes which cannot be implemented by the above 2 rules. 8) What are the Various Master and Detail Relation ships. The various Master and Detail Relationship are a) NonIsolated : The Master cannot be deleted when a child is exisiting b) Isolated : The Master can be deleted when the child is exisiting c) Cascading : The child gets deleted when the Master is deleted. 9) What are the Various Block Coordination Properties The various Block Coordination Properties are a) Immediate Default Setting. The Detail records are shown when the Master Record are shown. b) Deffered with Auto Query Oracle Forms defer fetching the detail records until the operator navigates to the detail block. c) Deffered with No Auto Query The operator must navigate to the detail block and explicitly execute a query 10) What are the Different Optimisation Techniques The Various Optimisation techniques are a) Execute Plan : we can see the plan of the query and change it accordingly based on the indexes b)Optimizer_hint: set_item_property('DeptBlock',OPTIMIZER_HINT,'FIRST_ROWS'); Select /*+ First_Rows */ Deptno,Dname,Loc,Rowid from dept where (Deptno > 25) Page 44 of 74
- 45. c) Optimize_Sql : By setting the Optimize_Sql = No, Oracle Forms assigns a single cursor for all SQL statements.This slow downs the processing because for evertime the SQL must be parsed whenver they are executed. f45run module = my_firstform userid = scott/tiger optimize_sql = No d) Optimize_Tp : By setting the Optimize_Tp= No, Oracle Forms assigns seperate cursor only for each query SELECT statement. All other SQL statements reuse the cursor. f45run module = my_firstform userid = scott/tiger optimize_Tp = No 11) How do u implement the If statement in the Select Statement We can implement the if statement in the select statement by using the Decode statement. e.g select DECODE (EMP_CAT,'1','First','2','Second'Null); Here the Null is the else statement where null is done . 12) How many types of Exceptions are there There are 2 types of exceptions. They are a) System Exceptions e.g. When no_data_found, When too_many_rows b) User Defined Exceptions e.g. My_exception exception When My_exception then 13) What are the inline and the precompiler directives The inline and precompiler directives detect the values directly 14) How do you use the same lov for 2 columns We can use the same lov for 2 columns by passing the return values in global values and using the global values in the code 15) How many minimum groups are required for a matrix report The minimum number of groups in matrix report are 4 16) What is the difference between static and dynamic lov The static lov contains the predetermined values while the dynamic lov contains values that come at run time 17) What are snap shots and views Snapshots are mirror or replicas of tables. Views are built using the columns from one or more tables. The Single Table View can be updated but the view with multi table cannot be updated 18) What are the OOPS concepts in Oracle. Oracle does implement the OOPS concepts. The best example is the Property Classes. We can categorise the properties by setting the visual attributes and then attach the property classes for the objects. OOPS supports the concepts of objects and classes and we can consider the peroperty classes as classes and the items as objects 19) What is the difference between candidate key, unique key and primary key Candidate keys are the columns in the table that could be the primary keys and the primary key is the key that has been selected to identify the rows. Unique key is also useful for identifying the distinct rows in the table. 20) What is concurrency Cuncurrency is allowing simultaneous access of same data by different users. Locks useful for accesing the database are a) Exclusive The exclusive lock is useful for locking the row when an insert,update or delete is being done.This lock should not be applied when we do only select from the row. b) Share lock We can do the table as Share_Lock as many share_locks can be put on the same resource. 21) Previleges and Grants Previleges are the right to execute a particulare type of SQL statements. eg. Right to Connect, Right to create, Right to resource Grants are given to the objects so that the object might be accessed accordingly.The grant has to be given by the owner of the object. 22) Table Space,Data Files,Parameter File, Control Files Table Space : The table space is useful for storing the data in the database.When a database is created two table spaces are created. a) System Table space : This data file stores all the tables related to the system and dba tables b) User Table space : This data file stores all the user related tables Page 45 of 74
- 46. We should have seperate table spaces for storing the tables and indexes so that the access is fast. Data Files : Every Oracle Data Base has one or more physical data files.They store the data for the database.Every datafile is associated with only one database.Once the Data file is created the size cannot change.To increase the size of the database to store more data we have to add data file. Parameter Files : Parameter file is needed to start an instance.A parameter file contains the list of instance configuration parameters e.g.:: db_block_buffers = 500 db_name = ORA7 db_domain = u.s.acme lang Control Files : Control files record the physical structure of the data files and redo log files. They contain the Db name, name and location of dbs, data files ,redo log files and time stamp. 23) Physical Storage of the Data The finest level of granularity of the data base are the data blocks. Data Block : One Data Block correspond to specific number of physical database space Extent : Extent is the number of specific number of contigious data blocks. Segments : Set of Extents allocated for Extents. There are three types of Segments a) Data Segment : Non Clustered Table has data segment data of every table is stored in cluster data segment b) Index Segment : Each Index has index segment that stores data c) Roll Back Segment : Temporarily store 'undo' information 24) What are the Pct Free and Pct Used Pct Free is used to denote the percentage of the free space that is to be left when creating a table. Similarly Pct Used is used to denote the percentage of the used space that is to be used when creating a table eg. Pctfree 20, Pctused 40 25) What is Row Chaining The data of a row in a table may not be able to fit the same data block.Data for row is stored in a chain of data blocks . 26) What is a 2 Phase Commit Two Phase commit is used in distributed data base systems. This is useful to maintain the integrity of the database so that all the users see the same values. It contains DML statements or Remote Procedural calls that reference a remote object. There are basically 2 phases in a 2 phase commit. a) Prepare Phase : Global coordinator asks participants to prepare b) Commit Phase : Commit all participants to coordinator to Prepared, Read only or abort Reply 27) What is the difference between deleting and truncating of tables Deleting a table will not remove the rows from the table but entry is there in the database dictionary and it can be retrieved But truncating a table deletes it completely and it cannot be retrieved. 28) What are mutating tables When a table is in state of transition it is said to be mutating. eg :: If a row has been deleted then the table is said to be mutating and no operations can be done on the table except select. 29) What are Codd Rules Codd Rules describe the ideal nature of a RDBMS. No RDBMS satisfies all the 12 codd rules and Oracle Satisfies 11 of the 12 rules and is the only Rdbms to satisfy the maximum number of rules. 30) What is Normalisation Normalisation is the process of organising the tables to remove the redundancy.There are mainly 5 Normalisation rules. a) 1 Normal Form : A table is said to be in 1st Normal Form when the attributes are atomic b) 2 Normal Form : A table is said to be in 2nd Normal Form when all the candidate keys are dependant on the primary key c) 3rd Normal Form : A table is said to be third Normal form when it is not dependant transitively 31) What is the Difference between a post query and a pre query A post query will fire for every row that is fetched but the pre query will fire only once. 32) Deleting the Duplicate rows in the table We can delete the duplicate rows in the table by using the Rowid 33) Can U disable database trigger? How? Page 46 of 74
- 47. Yes. With respect to table ALTER TABLE TABLE [[ DISABLE all_trigger ]] 34) What is pseudo columns ? Name them? A pseudocolumn behaves like a table column, but is not actually stored in the table. You can select from pseudocolumns, but you cannot insert, update, or delete their values. This section describes these pseudocolumns: * CURRVAL * NEXTVAL * LEVEL * ROWID * ROWNUM 35) How many columns can table have? The number of columns in a table can range from 1 to 254. 36) Is space acquired in blocks or extents ? In extents . 37) what is clustered index? In an indexed cluster, rows are stored together based on their cluster key values . Can not applied for HASH. 38) what are the datatypes supported By oracle (INTERNAL)? Varchar2, Number,Char , MLSLABEL. 39 ) What are attributes of cursor? %FOUND , %NOTFOUND , %ISOPEN,%ROWCOUNT 40) Can you use select in FROM clause of SQL select ? Yes. GUI 1) What is a visual attribute? Visual attributes are the font, color, and pattern properties that you set for form and menu objects that appear in your application's interface. 2) Diff. between VAT and Property Class? imp Named visual attributes define only font, color, and pattern attributes; property classes can contain these and any other properties.You can change the appearance of objects at runtime by changing the named visual attribute programmatically; property class assignment cannot be changed programmatically. When an object is inheriting from both a property class and a named visual attribute, the named visual attribute settings take precedence, and any visual attribute properties in the class are ignored. 3 ) Which trigger related to mouse? * When-Mouse-Click * When-Mouse-DoubleClick * When-Mouse-Down * When-Mouse-Enter * When-Mouse-Leave * When-Mouse-Move * When-Mouse-Up 4) What is Current record attribute property? Specifies the named visual attribute used when an item is part of the current record. Current Record Attribute is frequently used at the block level to display the current row in a multi-record If you define an item-level Current Record Attribute, you can display a pre-determined item in a special color when it is part of the current record, but you cannot dynamically highlight the current item, as the input focus changes. 5) Can u change VAT at run time? Yes. You can programmatically change an object's named visual attribute setting to change the font, color, and pattern of the object at runtime. 6) Can u set default font in forms? Yes. Change windows registry(regedit). Set form45_font to the desired font. Page 47 of 74
- 48. 7) Can u have OLE objects in forms? Yes. 8) Can u have VBX and OCX controls in forms ? Yes. 9) What r the types of windows (Window style)? Specifies whether the window is a Document window or a Dialog window. 10) What is OLE Activation style property? Specifies the event that will activate the OLE containing item. 11) Can u change the mouse pointer ? How? Yes. Specifies the mouse cursor style. Use this property to dynamically change the shape of the cursor. 3.0 Data Base Administration 3.1 Introduction to DBA 1. What is a database instance ? Explain A database instance (server) is a set of memory structures and background processes that access a set of database files. The process can be shared by all users. The memory structures that are used to store most queried data from database. This helps us to improve database performance by decreasing the amount of I/O performed against data file. 2. What is parallel server? Multiple instances accessing the same database (Only in Multi-CPU environments). 3. What is Schema ? The set of objects owned by user account is called the schema 4. What is an Index ? How it is implemented in Oracle Database ? An index is a database structure used by the server to have direct access of a row in a table. An index is automatically created when a unique or primary key constraint clause is specified in create table command (Ver 7.0) 5. What is clustres ? Group of tables physically stored together because they share common columns and are often used together is called Clusters. 6. What is a cluster key ? The related columns of the tables are called the cluster key. The cluster key is indexed using a cluster index and its value is stores only once for multiple tables in the cluster. 7. What are the basic element of Base configuration of an oracle Database ? It consists of one or more data files one or more control files two or more redo log files The database contains Multiple users/schemas one or more rollback segments one or more tablespaces Data dictionary tables Page 48 of 74
- 49. User objects (tables,indexes,views etc) The server that access the database consists of SGA (Database buffer, Dictionary Cache Buffers, redo log buffers,Shared SQL pool) SMON PMON LGWR DBWR ARCH CKPT RECO Dispatcher User process with associated PGA 8. What is deadlock ? Explain. Two processes waiting to update the rows of a table which are locked by the other process then deadlock arises. In a database environment this will often happen because of not issuing proper row lock commands. Poor design of front-end application may cause this situation and the performance of server will reduce drastically. These locks will be released automatically when a commit/rollback operation performed or any one of this processes being killed externally. 3.2 Memory Management 9. What is SGA ? How it is different from Ver 6 and Ver 7 ? The System Global Area in a Oracle database is the area in memory to facilitates the transfer of information between users. It holds the most recently requested structural information about the database. The structure is Database buffers, Dictionary Cache, Redo Log Buffer and Shared SQL pool (Ver 7) area. 10. What is Shared SQL pool ? The data dictionary cache is stored in an area in SGA called the Shared SQL Pool. This will allow sharing of parsed SQL statements among concurrent users. 11. What is meant by Program Global Area (PGA) ? It is area in memory that is used by a Single Oracle User process. 12. What is a data segment ? Data segment are the physical areas within a database block in which the data associated with tables and clusters are stored. 13. What are the factors causing the reparsing of SQL statements in SGA ? Due to insufficient Shared SQL pool size Monitor the ratio of the reloads takes place while executing SQL statements. If the ratio is greater that 1 then increase the SHARED_POOL_SIZE. 3.3 Logical & Physical Architecture of Database 14. What is Database Buffers ? Database buffers are cache in the SGA used to hold the data blocks that are read from the data segments in the database such as tables, indexes and clusters. DB_BLOCK_BUFFERS parameter in INIT.ORA decides the size. 15. What is dictionary cache ? Dictionary cache is information about the database objects stored in a data dictionary table. Page 49 of 74
- 50. 16. What is meant by recursive hits ? Number of times processes repeatedly query the dictionary table is called recursive hits. It is due to the data dictionary cache is too small. By increasing the SHARED_POOL_SIZE parameter we can optimize the size of Data Dictionary Cache. 17. What is meant by redo log buffer ? Changes made to entries are written to the on-line redo log files so that they can be used in roll forward operation during database recoveries. Before writing them into the redo log files, they will first brought to redo log buffers in SGA and LGWR will write into files frequently. LOG_BUFFER parameter will decide the size. 18. How will you swap objects into a different table space for an existing database ? Export the user Perform import using the command imp system/manager file=export.dp indexfile=newfile.sql. This will create all definitions into newfile.sql. Drop necessary objects. Run the script newfile.sql after altering the tablespaces. Import from the backup for the necessary objects. 19. List the Optimal Flexible Architecture (OFA) of Oracle database ? or How can we organise the tablespaces in Oracle database to have maximum performance ? SYSTEM - Data dictionary tables DATA - Standard operational tables DATA2 - Static tables used for standard operations INDEXES - Indexes for Standard operational tables INDEXES1 - Indexes of static tables used for standard operations TOOLS - Tool table TOOLS1 - Indexes for tools table RBS - Standard Operations Rollback Segments RBS1,RBS2 - Additional/Special rollback segments TEMP - Temporary purpose tablespace TEMP_USER - Temporary tablespace for users USERS - User tablespaces. 20. How will you force database to use particular rollback segment ? SET TRANSACTION USE ROLLBACK SEGMENT rbs_name 21. What is meant by free extent ? A free extent is a collection of continuous free blocks in tablespace. When a segment is dropped its extents are reallocated and are marked as free. 22. How free extents are managed in Ver 6 and Ver 7. ? Free extents cannot be merged together in Ver 6.0 Free extents are periodically coalesces with the neighboring free extent Ver 7.0. 23. Which parameter in Storage clause will reduce no of rows per block ? PCTFREE parameter Row size also reduces no of rows per block. 24. What is significance of having storage clause ? We can plan the storage for a table as how much initial extents are required, how much can be extended next, how much % should leave free for managing row updations etc. 25. How does space allocation take place within a block ? Each block contains entries as follows : Fixed block header Page 50 of 74
- 51. Variable block header Row header, row date (Multiple rows may exists) PCTFREE (% of free space for row updation in future) 26. What is the role of PCTFREE parameter is Storage clause ? This is used to reserve certain amount of space in a block for expansion of rows. 27. What is the OPTIMAL parameter ? It is used to set the optimal length of rollback segment. 28. What is the functionality of SYSTEM tablespace ? To manage the database level of transactions such as modifications of the data dictionary table that record information about the free space usage. 29. How will you create multiple rollback segments in a database ? Create a database which implicitly creates a SYSTEM Rollback Segment in a SYSTEM tablespace. Create a Second Rollback Segment name R0 in the SYSTEM tablespace. Make new rollback segment available (After shutdown, modify init.ora file and Start database) Create other tablespace (RBS) for rollback segments. Create additional Rollback segment in tablespace (RBS) Deactivate Rollback Segment R0 and activate the newly created rollback segments. 30. How the space utilisation takes place within rollback segments ? It will try to fit the transaction in a cyclic fashion to all existing extents. Once it found an extent is in use then it forced to acquire a new extent. (No of extents is based on the OPTIMAL size). 31. Why query fails sometimes ? Rollback segment dynamically extent to handle larger transactions entry loads. A single transaction may wipeout all available free space in the Rollback Segment Tablespace. This prevents other user using Rollback segment. 32. How will you monitor the space allocation ? By querying DBA_SEGMENT table/View 33. How will you monitor rollback segment status ? Querying the DBA_ROLLBACK_SEGS view The status available as follows : IN USE - Rollback Segment is on-line AVAILABLE - Rollback Segment available bur not on-line OFF-LINE - Rollback Segment us off-line INVALID - Rollback Segment dropped NEEDS RECOVERY - Contains data but need recovery or corrupted PARTLY AVAILABLE - Contains data from an unresolved transaction involving a distributed database 34. List the sequence of events when a large transaction that exceeds beyond its optimal value when an entry wraps and causes the rollback segment to expand into another extend. Transaction Begins An entry is made in the RBS header for new transactions entry Transaction acquired blocks in an extent of RBS The entry attempts to wrap into second extent. None is available. So that the RBS must extent. The RBS checks to see if it is oldest inactive segment Oldest inactive segment is eliminated RBS extends The Data dictionary table for space management are updated Transaction Completes. Page 51 of 74
- 52. 35. How can we plan storage for very large tables ? Limit the number of extents in the table Separate the Table from its indexes Allocate sufficient temporary storage 36. How will you estimate the space required by non-clustered tables ? Calculate the total block header size Calculate the available data space per block Calculate the combined column length of the average row Calculate the total average row size Calculate the average number rows that can fit in a block Calculate the number of blocks and bytes required for the table After arriving the calculation add the additional space to calculate the initial extent size for working area 37. Is it possible to use raw devices as data file and what is the advantages over file system files ? Yes. The advantages over file system files : I/O will be improved because Oracle is bye-passing the kernal while writing into disk. Disk Corruption will be very less. 38. What is a control file ? Database's overall physical architecture is maintained in a file called control file. It will be used to maintain internal consistency and guide recovery operations. Multiple copies of control files are advisable. 39. How to implement the multiple control files for an existing database ? Shutdown the database Copy one of the existing control file to new location' Edit config.ora file by adding new control file name Restart the database 40. What is meant by Redo Log file mirroring ? How it can be achieved ? Process of having a copy of redo log files is called mirroring. This can be achieved by creating group of log files together, so that LGWR will automatically writes them to all the members of the current on-line redo log group. If any one group fails then database automatically switch over to next group. 41. What is advantage of having disk shadowing/Mirroring ? Shadow set of disks save as a backup in the event of disk failure. In most Operating System if any disk failure occurs it automatically switchover to place of failed disk. Improved performance because of most OS support volume shadowing can direct file I/O request to use the shadow set of files instead of the main set of files. This reduces I/O load on the main set of disks. 42. What is use of rollback segment in Database ? They allow the database to maintain read consistency between multiple transactions. 43. What is a Rollback segment entry ? It is the set of before image data blocks that contain rows that are modified by a transaction. Each Rollback Segment entry must be completed within one rollback segment. A single rollback segment can have multiple rollback segment entries. 44. What a hit ratio ? It is a measure of well the data cache buffer is handling requests for data. Hit Ratio = (Logical Reads - Physical reads - Hit Misses) / Logical reads. 45. When will be a segment released ? Page 52 of 74
- 53. When Segment is dropped. When Shrink (RBS only) When truncated (TRUNCATE used with drop storage option) 46. What are disadvantages of having raw devices ? We should depend on export/import utility for backup/recovery (fully reliable) The tar command cannot be used for physical file backup, instead we can use dd command which is less flexible and has limited recoveries. 47. List the factors that can affect the accuracy of the estimations ? The space used transaction entries and deleted records does not become free immediately after completion due to delayed cleanout. Trailing nulls and length bytes are not stored. Inserts of, updates to, and deletes of rows as well as columns larger than a single data block, can cause fragmentation and chained row pieces. 3.4 Database Security & Administration 48. What is user account in Oracle database ? An user account is not a physical structure in Database but it is having important relationship to the objects in the database and will be having certain privileges. 49. How will you enforce security using stores procedures ? Don't grant user access directly to tables within application Instead grant the ability to access the procedures that access the tables When procedure executed it will execute the privilege of procedures owner. Users cannot access tables except via the procedure. 50. What are the dictionary tables used to monitor a database spaces ? DBA_FREE_SPACE DBA_SEGMENTS DBA_DATA_FILES 51. What are responsibilities of a Database Administrator ? 1. Installing and upgrading the Oracle Server and application tools 2. Allocating system storage and planning future storage requirements for the database system. 3. Managing primary database structures(tablespaces) 4. Managing primary objects (table,views,indexes) 5. Enrolling users and maintaining system security 6. Ensuring compliance with Oracle license agreement 7. Controlling and monitoring user access to the database 8. Monitoring and optimising the performance of the database 9. Planning for backup and recovery of database information 10. Maintain archived data on tape 11. Backing up and restoring the database 12. Contacting Oracle Corporation for technical support 52. What are requirements one should fulfill to connect to ORACLE as internal? Operating system account has the operating system privileges that allow you to connect One should be authorised to connect as internal Database has a password for internal connections, and you know the password must use a dedicated server 53. What are the roles and user accounts created automatically with the database ? DBA role - Contains all database system privileges SYS user account - The DBA role will be assigned to this account. All of the base tables and views for the database's dictionary are store in this schema and are manipulated only by ORACLE. Page 53 of 74
- 54. SYSTEM user account - It has all the system privileges for the database and additional tables and views that display administrative information and internal tables and views used by oracle tools are created using the username. 54. What are the database administrators utilities available ? SQL*DBA - This allows DBA to monitor and control an ORACLE database. SQL*Loader - It loads data from standard operating system files (Flat files) into ORACLE database tables. EXPORT(exp) and IMPOER (imp) utilities allow you to move existing data in ORACLE format to and from ORACLE database. 55. What are the minimum parameters should exist in the parameter file (init.ora) ? DB_NAME - Must set to a text string of not more that 8 characters and it will be stored inside the datafiles, redo log files and control file while database creation. DB_DOMAIN - It is string that specifies the network domain where the database is created. The global database name is identified by setting these parameters (DB_NAME & DB_DOMAIN) CONTROL_FILES - List of control filenames of the database. If name is not mentioned then default name will be used. DB_BLOCK_SIZE - The default data block size and is operating system dependent. It cannot be changed after database creation except by re-creating the database. DB_BLOCK_BUFFERS - The maximum number of operating system processes that can be connected to ORACLE concurrently. The value should be 5 (background process) and additional 1 for each user. ROLLBACK_SEGMENTS - List of rollback segments an ORACLE instance acquires at database startup. Also optionally LICENSE_MAX_SESSIONS,LICENSE_SESSION_WARNING and LICENSE_MAX_USERS. 56. What is a trace file and how it is created ? Each server and background process can write an associated trace file. When an internal error is detected by a process or user process, it dumps information about the error to its trace. This can be used for tuning the database. 57. What are roles ? How can we implement roles ? Roles are easiest way to grant and manage common privileges needed by different groups of database users. Creating roles and assigning privies to roles. Assign each role to group of users. This will simplify the job of assigning privileges to individual users. 58. What are the steps to switch a database's archiving mode between NOARCHIEVELOG and ARCHIVELOG mode ? 1. Shutdown the database instance 2. Backup the database 3. Perform any operating system specific steps (optional) 4. Start up a new instance and mount but do not open the database 5. Switch the database's archiving mode. 59. How can you enable automatic archiving ? Shut the database Backup the database Modify/Include LOG_ARCHIVE_START = TRUE in init.ora file Start up the database 60. How can we specify the Archived log file name format and destination ? By setting the following values in init.ora file LOG_ARCHIVE_FORMAT = arch%S/s/T/t.arc (%S - Log sequence number and is zero left-paded, %s - Log sequence number not paded, %T - Thread number left-zero-paded and %t - Thread number not paded). The file name created is arch0001.arc %S is used. LOG_ARCHIEVE_DEST = path Page 54 of 74
- 55. Shut the database and change these parameters in init.ora files. 61. What is the user of ANALYZE command ? To perform one of these function on an index, table, or cluster : to collect statistics about object used by the optimizer and store them in the data dictionary. to delete statistics about the object from the data dictionary to validate the structure of the object to identify migrated and chained rows of the table or cluster. 3.5 Managing Distributed Databases 62. How can we reduce the network traffic ? Replication of data in distributed environment Using snapshots to replicate data Using remote procedure calls. 63. What is a snapshot ? Snapshot is an object used to dynamically replicate data between distributed databases at specified time intervals. In ver 7.0 they are read only. 64. What are the various type of snapshots ? Simple and Complex. 65. Differentiative simple and complex, snapshots A simple snapshot is based on a query that does not contains GROUP BY clauses, CONNECT by clauses, JOINs, Subquery or a set of operations. A complex snapshots contain at least any one of the above. 66. What is dynamic data replication ? Updating or inserting records in remote database through database triggers. It may fail if remote database is having any problem. 67. How can you enforce referential integrity in snapshots ? Time the references to occur when master tables are not in use. Perform the references manually immediately after locking the master tables. We can join tables in snapshots by creating a complex snapshot that will be based on the master tables. 68. What are the options available to refresh snapshots ? COMPLETE - Tables are completely regenerated using the snapshot's query and the master tables every time the snapshot referenced. FAST - If simple snapshot used then a snapshot log can be used to send only the changes to the snapshot tables. FORCE - The default value. If possible it performs a FAST refresh; Otherwise it will perform a COMPLETE refresh. 69. What is a snapshot tag ? It is a table that maintains a record of modifications to the master table in a snapshot. It is stored in the same database as master table and is only available for simple snapshots. It should be created before creating snapshots. 70. When will the data in the snapshot log be used ? The data in the snapshot log is used during fast references of the table's snapshots. 71. What are the pre-requisites to create a snapshot log ? We must be able to create a after row trigger on table (i.e. it should not be already available) After giving table previleges. Page 55 of 74
- 56. We cannot specify snapshot log name because oracle uses the name of the master table in the name of the database objects that support its snapshot log. The master table name should be less than or equal to 23 characters. (The table name created will be MLOG$_tablename, and trigger name will be TLOG$_tablename) 72. What are the benefits of distributed options in databases ? Database on other servers can be updated and those transactions can be grouped together with others in a logical unit. Database uses a two phase commit 73. What is a two-phase commit ? Database on other servers can be updated and those transactions can be grouped together with others in a logical unit is called two-phase commit. They are The Preparation Phase : An initiating node called the global coordinator notifies all sites involved in the transaction to be ready either commit or rollback the transaction. The Commit Phase : If there is no problem with prepare phase, then all sites commit their transactions. If a network or node failure occurs, then all sites rollback their transactions. 3.6 Managing Backup & Recovery 74. What are the different methods of backing up oracle database ? Logical Backups Cold Backups Hot Backups (Archive log) 75. What is a logical backup ? Logical backup involves reading a set of database records and writing them into a file. Export utility is used for taking backup and Import utility is used to recover from backup. 76. What is cold backup ? What are the elements of it ? Cold backup is taking backup of all physical files after normal shutdown of database. We need to take All Data files All Control files All on-line redo log files Then init.ora file (optional) 77. What are the different kind of export backups ? Full backup - Complete database Incremental Backup - Only affected tables from last incremental date / Full backup date Cumulative backup - Only affected table from the last cumulative date / Full backup date 78. What is hot backup and how it can be taken ? Taking backup of archive log files when database is open. For this the ARCHIVELOG mode should be enabled. The following files need to be backed up : All data files All archive log, redo log files On control file. 79. What is the use of FILE option in EXP command ? To give the export file name. 80. What is the use of COMPRESS option in EXP command ? Flag to indicate whether export should compress fragmented segments into single extents. 81. What is the use of GRANT option in EXP command ? Page 56 of 74
- 57. A flag to indicate whether grants on database objects will be exported or not. Values is 'Y' or 'N'. 82. What is the use of INDEXES option in EXP command ? A flag to indicate whether indexes on tables will be exported. 83. What is use of ROWS option in EXP command ? Flag to indicate whether table rows should be exported. If 'N' only DDL statements for the database objects will be created. 84. What is the use of CONSTRAINTS option in EXP command ? A flag to indicate whether constraints on table need to be exported. 85. What is the use of FULL option in EXP command ? A flag to indicate whether full database export should be performed. 86. What is the use of OWNER option in EXP command ? List of table accounts should be exported. 87. What is the use of TABLES option in EXP command ? List of tables should be exported. 88. What is use of RECORD LENGTH option in EXP command ? Record length in bytes. 89. What is use of INCTYPE option in EXP command ? Type export should be performed. COMPLETE, CUMULATIVE, INCREMENTAL 90. What is use of RECORD option in EXP command ? For incremental exports, the flag indicates whether a record will be stored in data dictionary tables recording the export. 91. What is the use of PARFILE option in EXP command ? Name of the parameter file to passed for export. 92. What is the use of ANALYSE (Ver 7) option in EXP command ? A flag to indicate whether statistical information about the exported objects should be written to export dump file. 93. What is use of CONSISTENT (Ver 7) option in EXP command ? A flag to indicate whether a read consistent version of all the exported objects should be maintained. 94. What is the use of Log (Ver 7) option in EXP command ? The name of file to which log of the export will be written. 95. What is use of FILE option in IMP command ? The name of file from which import should be performed. 96. What is the use of SHOW option in IMP command ? A flag to indicate whether file content should be displayed or not. 97. What is the use of IGNORE option in IMP command ? A flag to indicate whether import should ignore errors encounter when issuing CREATE command. Page 57 of 74
- 58. 98. What is the use of GRANT option in IMP command ? A flag to indicate whether grants on database objects will be imported. 99. What is use of INDEXES option in IMP command ? A flag to indicate whether import should import index on tables or not. 100. What is use of ROWS option in IMP command ? A flag to indicate whether rows should be imported. I f this is set to 'N' then only DDL for the database objects will be executed ? 101. What is the use of FULL option in IMP command ? A flag to indicate whether full import should be done or not. 102. What is the use of FROMUSER option in IMP command ? A list of database accounts whose objects should be read from the export dump file. 103. What is use of TOUSER option in IMP command ? A list of database accounts into which objects in the export dump file will be imported 104. What is use of TABLES option in IMP command ? A list of tables to be imported. 105. What is use of RECORDLENGTH option in IMP command ? The length of the record in bytes of the export dump file. 106. What is use of INCTYPE option in the IMP command ? The type of import being performed. 107. What is use of COMMIT option in IMP command ? A flag to indicate whether import should commit after each array. If 'N' then commit will take place at table level 108. What is use of PARFILE option in IMP command ? Name of the parameter file to passed for import command. 109. What is use of INDEXFILE option in IMP command ? If filename is given then all the DDL will be created in the given file. 110. What is use of DESTROY (Ver 7) option in IMP command ? A flag to indicate whether the create tablespace command found in dump files from full exports will be executed. 111. What is use of LOG option in IMP command ? Name of the file to which the log of the import will be written. 112. Consider a case below : User is taking the backup in the following fashion : Type F I I I I C I I I I C I I Date 1 2 3 4 5 6 7 8 9 10 11 12 13 F - Full Backup I - Incremental Backup C - Cumulative Backup Suppose database crash on 14th morning. How can we retrieve the database ? Page 58 of 74
- 59. Create the database Import from the Full backup which was taken on 1st Import from Cumulative backups which was taken on 6th Import from Cumulative backups which was taken on 1th Import from the Incremental backups 12,13 respectively. Now the database will be available to latest status provided there is no transaction taken place after the 13th incremental backup. 113. List the steps to restore the database if data file lost. (Assume we are taking hot backups) Copy the lost file from the backup to the original location Start the instance Mount the database Recover the database using recover database command Open the database 114. What are the points to be taken care when we are using SQL*Loader for importing data from flat files ? Whether table and indexes are properly sized. Direct option being used or not (Ver 7) If one time load do not create any index until data has been loaded and table size is verified. 115. What are the advantages of using direct path option in SQL*Loader ? It bypasses the normal processing of insert statements and instead writes directly to tables data blocks. When direct option is used index become invalid and once the load complete the new key is merged with all old one and bring the status to valid. Data should be presorted otherwise it needs the double the size in tablespace. 116. What are areas a DBA can monitor the database using SQLDBA command? DBA can monitor the following areas to do fine tuning of the database : Processes Sessions Tables(Locks etc) SQL Area Library Cache Latch Locks File I/O System I/O Rollback Segments Statistics (System, Sessions) Apart from this all DBA activities can be performed through SQLDBA command. DDE ¡V OLE DDE - Dynamic Data Exchange. DLL - Dynamic Link Library OLE - Object Linking and Embedding. MAPI ¡V Messaging Application Program Interface What is DDE ? DDE is method for Inter Process Communication. An inter process communication is a method of passing data between processes and synchronising events. How does DDE work ? DDE uses shared memory to exchange data and a protocol to synchronize passing of data. What does a DLL contain ? A DLL contains code, data and windows resources. Page 59 of 74
- 60. How does a DLL work ? A DLL allocates a global memory block to an application and uses this to exchange data with application. What are the two types of DDE application ? Message based DDE applications and Dynamic Data Exchange Management Library application. What are the parts of a DDE application ? Client application, Server application, Client/Server application and Monitor application. What is a monitor application in the context of DDE ? A monitor application can only intercept messages but cannot act on it. What is the use of a monitor application ? A monitor application can be used as a debugging tool. What is the connection between OLE and DDE ? OLE is a set of DDE executable commands to which DDE protocol is applicable. What is the difference between an embedded object and a linked object ? An embedded object is stored in the document itself while the document just stores a reference to the linked object. If a link object is changed independently of the document, wht happens the linked object in the document ? 1. The reference object is automatically refreshed 2. The reference object is not refreshed 3. The user decides whether the object is to refreshed or if the older version is retained. Answer is 2 What are the types of OLE applications ? Client, Server and Object handlers. What is an object handler ? An Object handler is a set of DLL that facilitate communication between client application and server application. What are the advantages of OLE ? No need to switch between applications. Facilitate the use of specialized applications to create objects which can be embedded. What is the difference between a stored procedure and a database trigger ? A trigger is automatically executed when the firing event occurs while stored procedure has to be invoked. Oracle Forms: 1. How to use single data block to query multiple tables 2. How to see the select statement when we issue execute_query 3. What are the system variables can be changed 4. How do you trap default forms processing ( DML) 5. What is the difference between post-query and post-select 6. What is purpose and order of firing the following triggers 1. on fetch 2. on select 7. What is the number of records buffered and Query array size properties of data block 8. What is the difference between object libraries and object groups 9. What is the difference between pre-query and pre-select triggers 10. What is the difference between pre-text-item and when-new-item-instance triggers Page 60 of 74
- 61. 11. What is the order of firing the following triggers 1. when-new-form-instance 2. pre-text-item (Both are in form-level) 12. What is the validation unit property of form module 13. What is the order of checking for a program unit from form module(local program unit, library, stored procedure) 14. What is the difference between PL/SQL library and object library 15. what is the use of pre text/pre record/pre form 16. types of record groups and usage 17. what is id_null function 18. what is the return data types of id_null, show_alert, show_lov 19. what is the difference between call_form , open_form, new_form Which is restricted built-in and why? Which can¡Št issue savepoint What is session parameter of open_form? 20. which are the triggers will fire in the following situation I have three text items 1. Text-item1 1.key-next-item Go_item (¡¥text_item2¡Š); Go_item (¡¥text_item3¡Š); 2. Text-item2 1. Pre-text-item 2. When-validate-item 3. When-new-item-instance 4. Key-next-item 5. Post-text-item 6. Post-change 3. Text-item3 1. Pre-text-item 2. When-validate-item 3. When-new-item-instance 4. Key-next-item 5. Post-text-item 6. Post-change If I press tab or enter key at text-item1 what are the triggers will fire and order of firing during the entire navigation. If I change key-next-item trigger of text-item1 Go_item (¡¥text_item2¡Š); : Text_item2: = ¡¥Nagendra¡Š; Go_item (¡¥text_item3¡Š); Then what are the triggers will fire and order of firing 21. What is synchronous and asynchronous parameters for run_product built-in 22. How do you suppress the logon screen while running the form for the first time 23. What is primary canvas property of window and where it will be useful 24. I have when-button-pressed trigger at form , block and item level If I want to execute first block, form then item level trigger what changes I have to make. 25. what is data parameter and text parameter 26. Can we re-generate a library that is currently accessing by some other session 27. Can we re-generate and save a library that has been attached with some forms but they are running currently. 28. Can we re-generate a library that has been attached with some forms , will the changes will reflect in the referenced forms 29. What is the use of transactional triggers 30. Can we modify a sub classed object ( from object group and from object libraries) 31. How to set forms default directory 32. What is the return data type of populate_group built-in 33. What is the difference between OLE object created at design time and runtime 34. Will the timer will expire during large query executing Page 61 of 74
- 62. 35. What is the built-in package available to manipulate text files( forms) 36. Can we define a relation between two control blocks 37. If we change relation property from non-isolated to cascading what changes will occur 38. What is the coordination property of a relation 39. If we delete on-clear-details trigger in a relation what happens 40. What is the first trigger fires when we run a form 41. What is the use of enforce primary key property of data block 42. Can we put items other than buttons in the toolbars 43. Which object relates content and stacked canvases(window) 44. How to navigate from one form to other form(built-in) 45. How to copy values from list item to record group 46. In a non-isolated relation what is the order of firing the following triggers 1. on-populate-details 2. on-clear-details 3. pre-query 4. pre-select 47. How to find out the previous form id in multi form application(it¡Šs system variable) 48. How to use single LOV for multiple items Oracle reports: 1. Minimum requirement to make a matrix report (Queries, Groups and Repeating frames) 2. How to change the font of an field at runtime based on the value 3. What is the anchoring and enclosing object 4. What is anchor object 5. How to rotate a field( data base field in the layout) 6. What is the difference between lexical and bind parameters 7. What is the place holder 8. What is the use of frame(not repeating) 9. What is the use of format triggers 10. SRW package 11. What is flex mode and confine mode 12. what difference between the logical and physical pages and planes 13. what is the use of group filter SQL and PL/SQL 1. Queries for Nth maximum ,Nth row 2. what is use of the index ( maximum try to cover) 3. Select the departments whose sum of the salary greater than the sum of salaries of any department? 4. What is implicit cursors 5. What is public synonyms and uses 6. When index will be used in the query 7. What is the result of the following queries 1. Select * from emp where Comm in (null); 2. Select * from emp where Comm = null; 3. Select * from emp where Comm = ¡¥¡Š; 4. Select * from emp where Comm is ( select null from dual); 8. Query to display employee name and his managers name 9. Query to find the employees who is having more then one subordinate 10. Query to find the employees whose salary is greater then his department average salary 11. Query to display employees salary as 2000 for department 20 and rest as their salaries 12. Query to display no of employees in the department 10, 20,30 in a single row Output Dept10 dept20 dept30 256 13. Query to find the no of subordinate levels for given manager 14. Query to find the no of employees who is drawing less than 1500 and greater than 2000 Server concepts 1. what are the physical database components 2. what are the logical database components Page 62 of 74
- 63. 3. what is row chaining 4. what is the relation between oracle data block ,extents and segments 5. how many types of segments are there 6. what is temporary segments 7. what is redo log 8. what is the difference between rollback segments and redo log files 9. what is the difference between database buffers and redo log buffer of SGA 10. 1) How delete duplicate records in a table delete from emp where rowid not in (select max(rowid) from emp group by empno); 2) How to make a column into not null column. Ans: alter table emp modify (empno not null); ->this can be done only when all the values in empno are non null (i.e not empty) ?h To make a not null column into null column alter table emp modify (empno null); The fallowing are the rules for i. adding null or not null property >You may change a column¡Šs null property to not null only when that field does contain null values(i. It can¡Št be empty) >At any time you may change a column¡Šs not null property to null ii. adding a colum to a table >You may add a column at any time if NOT NULL isn¡Št specified (i.e when new column can accept null values ) >You may add a NOT NULL column in three steps. a. Add the column without NOT NULL specified. b. Fill every row in that column with data. c. Modify the column to be NOT NULL. iii. modifying a column >You can increase a CHAR column¡¥s width at any time. >You can increase the number of digits and the number of decimal places in a NUMBER column at any time >To CHANGE data types or to DECREASE column¡Šs width the column should be null for every row 3)Write queries for the fallowing ex. select * from emp_self; EMP_NO EMPN_NAME SAL MGR DEPTID --------- -------------------- ---------- ---------- ---------- 400 jane 20000 110 20 102 Mary 19000 110 20 101 charles 8000 105 50 104 Linda 9000 100 10 110 john 25000 105 20 105 newton 2000 50 100 ALEN 15000 105 50 200 BORIS 3000 110 20 103 DAVID 10000 100 10 300 monica 7000 105 50 i) Query to get the employees who are working under mgr with salary > 10000 select emp_no,mgr from emp_self where mgr in (select emp_no from emp_self where sal > 10000); ii) Query to get the employees who are getting salaries more than their managers select a.emp_no from emp_self a,emp_self b where a.mgr =b.emp_no and a.sal > b.sal; EMP_NO ------- 101 100 110 300 iii) Query to find the nth highest salary select a.empn_name,a.sal from emp_self a where &n = (select count(*) from emp_self b where a.sal < b.sal); Page 63 of 74
- 64. When n=1 , sal =20000 ->second highest salary ; n=4 , sal =10000 ->fifth highest salary ; iv) Query to find the second highest salary in different departments. select a.deptid,min(a. sal) from emp_self a where 1 in (select count(*) from emp_self b where a.sal < b.sal group by b.deptid) group by a.deptid; DEPTID MIN(A.SAL) ------- ---------- 10 9000 20 20000 50 8000 v) Query to find departments with total salary >25000 select deptid from emp_self having sum(sal) >25000 group by deptid; DEPTID ------ 20 50 4) study the fallowing pl/sql block and find the type of error ->syntax,semantic(logical) or precedence begin for i in 1..5 loop update emp set sal = 1000 where empno =100 ; end loop; end; 5) Difference between (MAX,MIN) and (GREATEST ,LEAST) The functions max and min compares different rows . Whereas greatest and least work on a group of columns ,either actual or calculated values within a single row. Ex. select * from emp_self; EMP_NO EMPN_NAME SAL MGR ------ -------------------- ------- ---------- 100 alen 9,000 105 200 boris 10,000 110 101 charles 8,000 105 SQL> select max(sal),min(sal) from emp_self; MAX(SAL) MIN(SAL) ---------- ---------- 10000 8000 SQL> select greatest(sal),least(sal) from emp_self; GREATEST(SAL) LEAST(SAL) ------------- ---------- 9000 9000 10000 10000 8000 8000 6)Different kinds of constraints . 6)Where Procedures,Functions and Triggers are stored ?. 7)What are the improtant differences between Procedures,Functions and Triggers ?. 8)Can we call a Procedure from a Trigger ?. 9)what are packages ?. 9)What are the different kinds of parameters ?. 10)Can we return a OUT parameter from a procedure ?. 11)Differences between ROWNUM and ROWID . 12)How do you handle exceptions ?. 12)How many system defined exceptions are there ?. 13)How do you write user defined message for all the system defined exceptions. 14)Difference between Commit and H(?)ost . 15)Differences between delete ,truncate and drop commands . 16) How do you display messages in the backend procedure ?. Page 64 of 74
- 65. 17) why can¡Št you use create/drop while declaring a trigger ?. 18)Advantages of union over joins . 19)Definitions of commit, rollback, save point 20)Difference between truncate and delete (truncate =delete + commit) 1)Name the five global report triggers i. before report ii. after report iii. between pages iv. before parameter form v.after parameter form As a general rule, any processing that will affect the data retrieved by the report should be performed in the Before Parameter Form or After Parameter Form triggers. (These are the two report triggers that fire before anything is parsed or fetched.) Any processing that will not affect the data retrieved by the report can be performed in the other triggers. Report Builder has five global report triggers. You cannot create new global report triggers. The trigger names indicate at what point the trigger fires: Before Report Fires before the report is executed but after queries are parsed. After Report Fires after you exit the Previewer, or after report output is sent to a specified destination, such as a file, a printer, or an Oracle Office userid. This trigger can be used to clean up any initial processing that was done, such as deleting tables. Note, however, that this trigger always fires, whether or not your report completed successfully. Between Pages Fires before each page of the report is formatted, except the very first page. This trigger can be used for customized page formatting. In the Previewer, this trigger only fires the first time that you go to a page. If you subsequently return to the page, the trigger does not fire again. Before Parameter Form Fires before the Runtime Parameter Form is displayed. From this trigger, you can access and change the values of parameters, PL/SQL global variables, and report-level columns. If the Runtime Parameter Form is suppressed, this trigger still fires. Consequently, you can use this trigger for validation of command line parameters. After Parameter Form Fires after the Runtime Parameter Form is displayed. From this trigger, you can access parameters and check their values. This trigger can also be used to change parameter values or, if an error occurs, return to the Runtime Parameter Form. Columns from the data model are not accessible from this trigger. If the Runtime Parameter Form is suppressed, the After Parameter Form trigger still fires. Consequently, you can use this trigger for validation of command line parameters or other data. 2) Name the different types of alerts note , stop ,caution 3)call_form ( ), new_form ( ) call_form ( ) :-Runs an indicated form while keeping the parent form active. Form Builder runs the called form with the same Runform preferences as the parent form. When the called form is exited Form Builder processing resumes in the calling form at the point from which you initiated the call to CALL_FORM. PROCEDURE CALL_FORM (formmodule_name VARCHAR2); New_form( ) :- Exits the current form and enters the indicated form. The calling form is terminated as the parent form. If the calling form had been called by a higher form, Form Builder keeps the higher call active and treats it as a call to the new form. Form Builder releases memory (such as database cursors) that the terminated form was using. Form Builder runs the new form with the same Runform options as the parent form. If the parent form was a called form, Form Builder runs the new form with the same options as the parent form. PROCEDURE NEW_FORM (formmodule_name VARCHAR2); 4) system.mode-> SYSTEM.MODE indicates whether the form is in Normal, Enter Query, or Fetch Processing mode. The value is always a character string. NORMAL Indicates that the form is currently in normal processing mode. ENTER-QUERY Indicates that the form is currently in Enter Query mode. QUERY Indicates that the form is currently in fetch processing mode, meaning that a query is currently being processed. Usage Notes Page 65 of 74
- 66. When using SYSTEM.MODE to check whether the current block is in Enter Query mode, be aware that if testing from a When-Button-Pressed trigger in a control block, Enter Query mode will never be entered, because the control block is not the current block. 4)What are important new(Advanced) features of Forms 6.0. 5)Different types of list boxes. 6)What are record groups ?. 7)In case of a block with multiple records how to display records on the screen without using cursors ?. 8)Can we access a row in the first block from second by referencing block name along with the rowid ?. 9)In case of a block with multiple records how do check where a user entering a duplicate record well before saving it ?. 10)How to take care of concurrency ?. 1. What is the size of Varchar in Oracle 8.0 ? a. 2000 b. 4000 c. 254 d. none of the above 2. What is the size of Varchar in Oracle 7.0 ? a. 2000 b. 4000 c. 254 d. none of the above 3. The default value the lpad function takes is a. a space (¡§ ¡§) b. an asterisk c. The default value is not optional d. None of the above 4. The no. of columns that may be used as composite primary key in oracle 8 a. 8 b. 16 c. 32 d. none of the above 5. which of the following is true about add_months a. we can pass a numerical value in first parameter b. we can pass a negative value in second parameter c. Both a & b d. None of the above 6. The latest date that can be stored in oracle 8 a. 31st Dec 4012 A.D b. 31st Dec 4011 A.D c. Dec 31st ,9999 d. None of the above. 7. What happens when the first date is greater than the second date that is passed to the months_between function in oracle 8. a. It gives an error b. It gives a negative value c. None of the above 8. Regarding the Summary query which of the following is true a. The order of the base column list in the select statement should be same in the Group by clause. b. The order of the base column list in the select statement need not be same in the Group by clause. c. None of the above 9. Regarding the Summary query which of the following is true a. All the base table columns selected in the select list should be specified in the Group by clause. b. All the base table columns selected in the select list need not be specified in the Group by clause. c. None of the above. 10. How do u mask the user from entering irrelevant data ? a. Synonym b. View c. Index d. sequence 11. What does the length function returns when applied to column of char datatype ? 12. Which of the following is true about the packages ? a. Package specification should contain return type of a function b. Package specification need not contain return type of a function c. Both a & b d. None of the above Page 66 of 74
- 67. 13. If the first parameter is negative, then second parameter a. need not be negative b. there is no such restrictions c. should be positive d. None of the above. 14. Which of the following is true about procedures a. The size of the parameter should be mentioned in a procedure. b. The size of the parameter should not be mentioned in a procedure c. Both a & b d. None of the above. 15. ¡§REFERENCING¡š in oracle 8 a. used to mention referential integrity b. used for creating views c. there is no such word in oracle 8 d. none of the above 16. If you want to restrict the user, to enter the same values that has been stored in other table then what constraint do u use? a. Entity integrity b. Referential Integrity c. Both a & b d. None of the above 17. Which of the following is true about NULL? a. when an arithmetic operation is performed on NULL, u will get the result as NULL b. NULL is same as 0. c. NULL is same as blank date. d. None of the above 18. For a DDL statement, which of the following is true a. A DDL statement is preceded and followed by commit. b. All the DML statements gets committed even when u get an error after writing DDL statement. c. Both a & b d. None of the above. 19. Which of the following is true for update clause? a. We can update two base tables simultaneously b. U can use a subquery in SET clause of the UPDATE statement. c. Both a & b d. None of the above 20. Which of the following is true for delete? a. Delete statement can be given without writing where clause. b. We can delete two tables simultaneously c. Both a & b d. None of the above 21. How do u rename a table ? a. Using alter command b. Using RENAME c. Dropping the table and creating once again d. None of the above. 22. In oracle 7 which of the following is true about manipulating the view a. View based on two base tables can be manipulated b. View having a column which contain operation can be manipulated c. Both a & b d. None of the above 23. In oracle 8 which of the following is true about manipulating the view a. View based on two base tables can be manipulated b. View having a column which contain operation can be manipulated c. Both a & b d. None of the above 24. Which of the following is true about packages a. We can write a procedure in package body which has not been specified in package specification. b. We cannot write a procedure in package body which has not been specified in package specification. c. Both a & b d. None of the above. 25. Which of the following is true about outer joins a. The outer join symbol should be present on any one side of the join. b. The outer join symbol may be present on both the sides of the join c. The outer join return the rows from the two tables that donot have matching records in other table. d. None of the above Page 67 of 74
- 68. 26. Which of the following is true about procedure and a function a. Procedure should return a value and a function may not return a value b. A function has to return a value and a procedure don¡Št have to c. Both a & b d. None of the above. 27. What does OFA stands for ? a. Oracle Flexible Architecture b. Oracle Financials Applications c. Optimal Flexible Architecture d. None of the above Oracle Questions ?h What is SQL*Plus and where does it come from? ?h How does one use the SQL*Plus utility? ?h What commands can be executed from SQL*Plus? ?h What are the basic SQL*Plus commands? ?h What is AFIEDT.BUF? ?h How does one restore session state in SQL*Plus? ?h What is the difference between @ and @@? ?h What is the difference between & and &&? ?h What is the difference between ! and HOST? ?h What is the difference between ? and HELP? ?h How does one enable the SQL*Plus HELP facility? ?h How can one disable SQL*Plus prompting? ?h How can one trap errors in SQL*Plus? ?h How does one trace SQL statement execution? ?h How can one prevent SQL*Plus connection warning messages? ?h How can uses be prevented from executing devious commands? ?h How can one disable SQL*Plus formatting? ?h Can one send operating system parameters to SQL*Plus? ?h Can one copy tables with LONG columns from one database to another? ?h Where can one get more info about SQL*Plus? What is SQL*Plus and where does it come from? SQL*Plus is a command line SQL and PL/SQL language interface and reporting tool that ships with the Oracle Database Client and Server. It can be used interactively or driven from scripts. SQL*Plus is frequently used by DBAs and Developers to interact with the Oracle database. SQL*Plus's predecessor was called UFI (User Friendly Interface). UFI was included in the first releases of Oracle, its interface was extremely primitive and anything but user friendly. How does one use the SQL*Plus utility? Start using SQL*Plus by executing the "sqlplus" command-line utility. Valid options are: userid/password@db -- Connection details /nolog -- Do not login to Oracle. You will need to do it yourself. -s or -silent -- start sqlplus in silent mode. Not recommended for beginners! @myscript -- Start executing script called "myscript" Look at this simple example: sqlplus /nolog SQL> connect scott/tiger SQL> select * from tab; SQL> disconnect SQL> exit What commands can be executed from SQL*Plus? One can enter three kinds of commands from the SQL*Plus command prompt: 1. SQL*Plus commands - SQL*Plus commands are used to set options for SQL*Plus, format reports, edit files, edit the command buffer, and so on. SQL*Plus commands do not interact with the database. These commands do not have to be terminated with a semicolon (;), as is the case with SQL commands. The rest of this page is dedicated to SQL*Plus commands, eg. SHOW USER 2. SQL commands - for more information see the Oracle SQL FAQ. Eg: SELECT * FROM TAB; 3. PL/SQL blocks - for more information see the Oracle PLSQL FAQ. Eg: BEGIN DBMS_OUTPUT.PUT_LINE('Hello World!'); END; / What are the basic SQL*Plus commands? Page 68 of 74
- 69. The following SQL*Plus commands are available: ACCEPT Get input from the user DEFINE Declare a variable (short: DEF) DESCRIBE Lists the attributes of tables and other objects (short: DESC) EDIT Places you in an editor so you can edit a SQL command (short: ED) EXIT or QUIT Disconnect from the database and terminate SQL*Plus GET Retrieves a SQL file and places it into the SQL buffer HOST Issue an operating system command (short: !) LIST Displays the last command executed/ command in the SQL buffer (short: L) PROMPT Display a text string on the screen. Eg prompt Hello World!!! RUN List and Run the command stored in the SQL buffer (short: /) SAVE Saves command in the SQL buffer to a file. Eg "save x" will create a script file called x.sql SET Modify the SQL*Plus environment eg. SET PAGESIZE 23 SHOW Show environment settings (short: SHO). Eg SHOW ALL, SHO PAGESIZE etc. SPOOL Send output to a file. Eg "spool x" will save STDOUT to a file called x.lst START Run a SQL script file (short: @) How does one restore session state in SQL*Plus? Look at the following example (Oracle8): SQL> STORE SET filename REPLACE SQL> (do whatever you like) SQL> @filename What is AFIEDT.BUF? AFIEDT.BUF is the SQL*Plus default edit save file. When you issue the command "ed" or "edit" without arguments, the last SQL or PL/SQL command will be saved to a file called AFIEDT.BUF and opened in the default editor. In the prehistoric days when SQL*Plus was called UFI, the file name was "ufiedt.buf", short for UFI editing buffer. When new features were added to UFI, it was the initially named Advanced UFI and the filename was changed to "aufiedt.buf" and then to "afiedt.buf". They presumably needed to keep the name short for compatibility with some of the odd operating systems that Oracle supported in those days. The name "Advanced UFI" was never used officially, as the name was changed to SQL*Plus before this version was released. You can overwrite the default edit save file name like this: SET EDITFILE "afiedt.buf" What is the difference between @ and @@? The @ (at symbol) is equivalent to the START command and is used to run SQL*Plus command scripts. A single @ symbol runs the script in your current directory, or one specified with a full or relative path, or one that is found in you SQLPATH or ORACLE_PATH. @@ will start a sqlplus script that is in the same directory as the script that called it (relative to the directory of the current script). This is normally used for nested command files. What is the difference between & and &&? "&" is used to create a temporary substitution variable and will prompt you for a value every time it is referenced. "&&" is used to create a permanent substitution variable as with the DEFINE command and the OLD_VALUE or NEW_VALUE clauses of a COLUMN statement. Once you have entered a value it will use that value every time the variable is referenced. Eg: SQL> SELECT * FROM TAB WHERE TNAME LIKE '%&TABLE_NAME.%'; What is the difference between ! and HOST? Both "!" and "HOST" will execute operating system commands as child processes of SQL*Plus. The difference is that "HOST" will perform variable substitution (& and && symbols), whereas "!" will not. (Note: use "$" under MVS, VMS, and Windows environments, not "!") What is the difference between ? and HELP? There is no difference. Both "?" and HELP will read the SYSTEM.HELP table (if available) and shows help text on the screen. To use the help facility, type HELP followed by the command you need to learn more about. For example, to get help on the SELECT statement, type: HELP SELECT How does one enable the SQL*Plus HELP facility? To enable HELP for SQl*Plus, run the supplied SQL and Loader scritps to create the Help table and to populate it. Look at this Unix example: cd $ORACLE_HOME/sqlplus/admin/help sqlplus system/manager @helptbl sqlplus system/manager @helpindx sqlldr system/manager control=plushelp.ctl sqlldr system/manager control=sqlhelp.ctl sqlldr system/manager control=plshelp.ctl If the HELP command is not supported on your operating system, you can access the help table with a simple script like this: Page 69 of 74
- 70. HELP.SQL: select info from system.help where upper(topic)=upper('&1') / How can one disable SQL*Plus prompting? If you run a script that contains "&" symbols SQL*Plus thinks that you want to prompt the user for a value. To turn this off: SET ESCAPE ON SET ESCAPE "" SELECT 'You & me' FROM DUAL; or SET DEFINE ? SELECT 'You & me' FROM DUAL; Note: You can disable substitution variable prompting altogether by issuing the SET DEFINE OFF commmand. How can one trap errors in SQL*Plus? Use the "WHENEVER OSERROR ..." to trap operating system errors and the "WHENEVER SQLERROR ..." command to trap SQL and PL/SQL errors. Eg: SQL> WHENEVER OSERROR EXIT 9 SQL> WHENEVER SQLERROR EXIT SQL.SQLCODE How does one trace SQL statement execution? 1. Run the PLUSTRCE.SQL script from the SYS database user. This script is located the in $ORACLE_HOME/sqlplus/admin. 2. Create a PLAN_TABLE using the UTLXPLAN.SQL script. This script is in $ORACLE_HOME/rdbms/admin. 3. Use the "SET AUTOTRACE ON" command to trace SQL execution. This will print the result of your query, an explain plan and high level trace information. Look at this example: SQL> set autotrace on SQL> select * from dual; D - X Execution Plan ---------------------------------------------------------- 0 SELECT STATEMENT Optimizer=CHOOSE 1 0 TABLE ACCESS (FULL) OF 'DUAL' Statistics ---------------------------------------------------------- 0 recursive calls 2 db block gets 1 consistent gets 0 physical reads 0 redo size 181 bytes sent via SQL*Net to client 256 bytes received via SQL*Net from client 3 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed How can one prevent SQL*Plus connection warning messages? When I go to SQl*Plus, I get the following errors: Error accessing PRODUCT_USER_PROFILE Warning: Product user profile information not loaded! You may need to run PUPBLD.SQL as SYSTEM This messages will stop appearing when you create the PRODUCT_USER_PROFILE table in the SYSTEM schema. This is performed by the PUPBLD.SQL script. Go to the $ORACLE_HOME/sqlplus/admin directory, connect as SYSTEM and run @PUPBLD from the sqlprompt. How can users be prevented from executing devious commands? Yes, command authorization is verified against the SYSTEM.PRODUCT_USER_PROFILE table. This table is created by the PUPBLD.SQL script. Note that this table is not used when someone signs on as user SYSTEM. Eg. to disable all users whose names starts with OPS$ from executing the CONNECT command: Page 70 of 74
- 71. SQL> INSERT INTO SYSTEM.PRODUCT_USER_PROFILE VALUES ('SQL*Plus', 'OPS$%', 'CONNECT', NULL, NULL, 'DISABLED', NULL, NULL); How can one disable SQL*Plus formatting? Issue the following SET commands to disable all SQL*Plus formatting: SET ECHO OFF SET NEWPAGE 0 SET SPACE 0 SET PAGESIZE 0 SET FEEDBACK OFF SET HEADING OFF SET TRIMSPOOL ON These settings can also be entered on one line, eg.: SET ECHO OFF NEWPAGE 0 SPACE 0 PAGESIZE 0 FEED OFF HEAD OFF TRIMSPOOL ON Can one send operating system parameters to SQL*Plus? One can pass operating system variables to sqlplus using this syntax: sqlplus username/password @cmdfile.sql var1 var2 var3 Parameter var1 will be mapped to SQL*Plus variable &1, var2 to &2, etc. Look at this example: sqlplus scott/tiger @x.sql '"test parameter"' dual Where x.sql consists of: select '&1' from &2; exit 5; Can one copy tables with LONG columns from one database to another? About the fastest way of copying data between databases and schemas are by using the SQL*Plus COPY statement. Look at this example: COPY FROM SCOTT/TIGER@LOCAL_DB TO SCOTT/TIGER@REMOTE_DB - CREATE IMAGE_TABLE USING - SELECT IMAGE_NO, IMAGE - FROM IMAGES; Interview questions: 1.query for self join. 2.deletion of duplicate rows. 3.post query trigger 4.pre query trigger 5.mastere ¡Vdetail relation 6.report triggers 7.report parameters. 8.format triggers in report. 9.order of triggering of when new item instance. 10. Page 71 of 74
- 72. Set 6 : DBA Tasks, Responsibilities and Skills Required DILBERT'S LAWS OF WORK: Don't be irreplaceable, if you can't be replaced, you can't be promoted. Topics DBA Responsibilities Required Skills Qualifications Typical Interview Questions -------------------------------------------------------------------------------- DBA Responsibilities: The job of the DBA seems to be everything that everyone else either doesn't want to do, or doesn't have the ability to do. DBAs get the enviable task of figuring out all of the things no one else can figure out. More seriously though, here is a list of typical DBA responsibilities: Installation, configuration and upgrading of Oracle server software and related products Evaluate Oracle features and Oracle related products Establish and maintain sound backup and recovery policies and procedures Take care of the Database design and implementation Implement and maintain database security (create and maintain users and roles, assign privileges) Perform database tuning and performance monitoring Perform application tuning and performance monitoring Setup and maintain documentation and standards Plan growth and changes (capacity planning) Work as part of a team and provide 7x24 support when required Perform general technical trouble shooting and give consultation to development teams Interface with Oracle Corporation for technical support. -------------------------------------------------------------------------------- Required Skills: Good understanding of the Oracle database, related utilities and tools A good understanding of the underlying operating system A good knowledge of the physical database design Ability to perform both Oracle and operating system performance tuning and monitoring Knowledge of ALL Oracle backup and recovery scenarios A good knowledge of Oracle security management A good knowledge of how Oracle acquires and manages resources A good knowledge Oracle data integrity Sound knowledge of the implemented application systems Experience in code migration, database change management and data management through the various stages of the development life cycle Page 72 of 74
- 73. A sound knowledge of both database and system performance tuning A DBA should have sound communication skills with management, development teams, vendors and systems administrators Provide a strategic database direction for the organisation A DBA should have the ability to handle multiple projects and deadlines A DBA should possess a sound understanding of the business -------------------------------------------------------------------------------- Qualifications: Must be certified as an Oracle DBA Preferably a BS in computer science or related engineering field Lots and lots of EXPERIENCE -------------------------------------------------------------------------------- Typical Interview Questions General Questions Tell us about yourself/ your background. What are the three major characteristics that you bring to the job market? What motivates you to do a good job? What two or three things are most important to you at work? What qualities do you think are essential to be successful in this kind of work? What courses did you attend? What job certifications do you hold? What subjects/courses did you excel in? Why? What subjects/courses gave you trouble? Why? How does your previous work experience prepare you for this position? How do you define 'success'? What has been your most significant accomplishment to date? Describe a challenge you encountered and how you dealt with it. Describe a failure and how you dealt with it. Describe the 'ideal' job... the 'ideal' supervisor. What leadership roles have you held? What prejudices do you hold? What do you like to do in your spare time? What are your career goals (a) 3 years from now; (b) 10 years from now? How does this position match your career goals? What have you done in the past year to improve yourself? In what areas do you feel you need further education and training to be successful? What do you know about our company? Why do you want to work for this company. Why should we hire you? Where do you see yourself fitting in to this organization . . .initially? . . .in 5 years? Why are you looking for a new job? How do you feel about re-locating? Are you willing to travel? What are your salary requirements? When would you be available to start if you were selected? General Oracle Questions Did you use online or off-line backups? What version of Oracle were you running? Haw many databases and what sizes? If you have to advise a backup strategy for a new application, how would you approach it and what questions will you ask? If a customer calls you about a hanging database session, what will you do to resolve it? Compare Oracle to any other database that you know. Why would you prefer to work on one and not on the other? Page 73 of 74
- 74. Oracle interview questions No answers, but these are useful questions for conducting Oracle interview. The readers are welcome to contribute their answers. What is an oracle instance? What is a view? What is referential integrity? Name the data dictionary that stores user-defined constraints? What is a collection of privileges? What is a snapshot? What is a synonym? What is a cursor? What is a sequence? What is a trigger? What is an exception? What is a partition of table? What are pseudo-columns in SQL? Provide examples. What are the Data Control statements? What is a schema? What is a type? What is a data model? What is a relation? Advantages of redo log files? What is an Archiver? What is a database buffer cache? What are the background processes in Oracle? %type and %rowtype are attributes for…? What are the steps in a two-phase commit? What is a union, intersect, minus? What is a join, explain the types of joins? What is a co-related sub-query? ODBC stands for…? Data-type used to work with integers is? Describe data models? Describe the Normalization principles? What are the types of Normalization? What is de-normalization? Page 74 of 74