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SEMI JOIN?
→ It returns row from first table when one or more row matched found in second table. →
→ Difference between semi-join and inner join is that row in first table will be returned only
once even if the second table contains two matches from a row in the first table, only one
copy of the row will be returned.
→ Semi-joins are written by using ‘IN’ & ‘EXISTS’ constructs.
ANTI JOIN?
→ It returns row from first table when no matches found in second table.
→ Anti-joins are written by using ‘NOT IN’ & ‘NOT EXISTS’ constructs.
Difference between Inner, Left outer, Right outer and Full outer joins?
Inner Join
Or Simple Join
Left Outer Join Right Outer Join Full Outer Join
Inner joins join the
multiple tables and
return those rows for
which the join
condition is true.
The inner join is the
most common join
among the types of
join.
The Left Outer Join
returns contain all
rows from the LEFT
table ( according to
the specified in ON
condition) and from
the other table
only those rows
where the joined
condition is true.
The RIGHT
OUTER JOIN
returns contain all
rows from the
RIGHT table
(according to the
specified in ON
condition) and from
the other table
only those rows
where the joined
condition is true.
The Full Outer Join
returns contain all
rows from the LEFT
table and RIGHT
table with null in
fields where the join
condition is not true.
SELECT column [ ,
column ] FROM t1
INNER JOIN t2
ON t1.column =
t2.column;
SELECT column [ ,
column ] FROM t1
LEFT [OUTER]
JOIN t2
ON t1.column =
t2.column;
SELECT column [ ,
column ] FROM t1
RIGHT [OUTER]
JOIN t2
ON t1.column =
t2.column;
SELECT column [ ,
column ] FROM t1
FULL [OUTER]
JOIN t2
ON t1.column =
t2.column;
The Oracle INNER
JOIN returns the
intersect records
of t1 and t2 as a
result.
The Oracle LEFT
OUTER JOIN
returns all the
records from t1 and
the intersect records
of t1 and t2 as a
result.
The Oracle RIGHT
OUTER JOIN
returns all the
records from t2 and
the intersect records
of t1 and t2 as a
result.
The Oracle FULL
OUTER JOIN
returns all the
records from t1 and
t2 tables as a result.](https://image.slidesharecdn.com/oraclequeans-210816121459/85/Paper-Presentation-of-SQL-and-PL-SQL-16-320.jpg)
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17
How can you fetch common data from 2 column?
ANS: we can fetch common data from two column by using Intersect or inner join
depending upon what actually you mean by common data.
Difference between Equi join & Outer join?
Equi Joins Outer Joins
Oracle Equi Joins retrieves the matching
column values of the multiple tables. The
join condition or the comparison operator
present in the WHERE clause of the select
statement.
Another type of joins is an outer
join which returns a result of an inner join
plus all the rows from one table for which
the join condition is not true.
SELECT column [ , column ] FROM t1 , t2
where t1.column = t2.column;
SELECT column [ , column ] FROM t1
LEFT | RIGHT | FULL [OUTER] JOIN
t2
ON t1.column = t2.column;
The Oracle Equijoin returns the intersect
records of t1 and t2 as a result.
There are three types of outer join as
given below:
Left Outer Joins (also called as Left Joins)
Right Outer Joins (also called as Right
Joins)
Full Outer Joins (also called as Full Joins)
AGGREGATE:
Count(*),Count(Coulmn) Will Be 0 If No Records But Max , Min Values Is Null
COUNT(COLUMN_NAME) COUNT(*)
Counts the entries in a column -
ignoring null values.
Counts the rows in table - including
null values.
Both are aggregate function or group
function.
Both are aggregate function or group
function.
Count(1) Count(*)
Counts The Rows In Table - Including
Null Values.
Counts The Rows In Table - Including
Null Values.
Counts Row By accessing An Index Counts Row Produced By Query
Fast, because it access index SLOW
Oracle Property ANSII standard](https://image.slidesharecdn.com/oraclequeans-210816121459/85/Paper-Presentation-of-SQL-and-PL-SQL-17-320.jpg)
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What is a foreign key?
Foreign key is a key used to link two tables together.
foreign key is field or a collection of field in one table that refers to the primary key in
another table. Table containing foreign key is called child table. Table containing candidate
key is called the reference or parent table.
• It is Referential Integrity (RI).
• It refers a primary (or) unique constraint of another table.
• It accepts null values in child records.
• It accepts duplicate values in child records.
• It is like a parent and child relationship.
A foreign key is specified as a key which is related to the primary key of another table. A
relationship needs to be created between two tables by referencing foreign key with the
primary key of another table. Foreign key acts like a cross-reference between tables as it
refers to the primary key of other table and the primary key-foreign key relationship is a very
crucial relationship as it maintains the ACID properties of database sometimes.
Integrity constraint violation :
child record found- delete.
parent record not found -insert.
On delete cascade:
It will delete parent record and corresponding child records also
On delete set null:
It will delete parent record and corresponding child record it’ll set null
What is a unique key?
• It is unique identifier.
• It accepts null values and can accept more than 1 null value.
• It is entity integrity.
• It is non – cluster index.
• It automatically generates unique index.
Unique key constraint uniquely identifies each record in the database. This key provides
uniqueness for the column or set of columns.
The Unique key cannot accept a duplicate value.
The unique key can accept only on Null value.
Not null key(C):
It ignores null value.
It is a domain integrity condition.
Check [C]:
It is a domain integrity
It should satisfy your condition.](https://image.slidesharecdn.com/oraclequeans-210816121459/85/Paper-Presentation-of-SQL-and-PL-SQL-29-320.jpg)
![33
33
VIEW MATERIALIZED VIEW
(i) A View is never stored it is only
displayed.
(i) A Materialized View is stored on the
disk.
(ii) View is the virtual table formed from
one or more base tables or views.
(ii) Materialized view is a SNAPSHOT
physical copy of the base table.
(iii) View is updated each time the virtual
table (View) is used.
(iii) Materialized View has to be updated
manually or using triggers.
(iv) Slow processing. (iv) Fast processing.
(v) View do not require memory space. (v) Materialized View utilizes memory
space.
(vi) No need log file. (vi) It will maintain log files.
(vii) Only select query has saved in data
dictionary table.
(vii) It will saves the output of the select
query in data dictionary table.
Types: simple, complex & force view Complete refresh , fast and force refresh
(viii) Syntax :-
Create View V As
(viii) Syntax:-
Create Materialized View V Build [clause]
Refresh [clause] On [Trigger] As
Without base table we can create table
using force view
Without base table we can not create MV
Index can not be created in views Index can be created in MV
Complete refresh Fast and force refresh
It truncate and reload new data Compare log file fetch remaining data
It is fast It is slow
DBMS_MVIEWS.REFRESH(‘MV_1,’C’); DBMS_MVIEWS.REFRESH(‘MV_1,’F’);
Force view:
• Not an existent table.
• No base table is necessary
• We can create a view with the dummy based table which does not exist in the
database.
• This view will be having errors.
• May be used for application code test.](https://image.slidesharecdn.com/oraclequeans-210816121459/85/Paper-Presentation-of-SQL-and-PL-SQL-33-320.jpg)
![48
48
Note:
• We can create a procedure inside anonymous block
• We can create procedure inside package
• We can create procedure inside procedure
• Used to business logic development
• May or may not have return value
Local procedure [private procedure]:
• Whenever you create a procedure inside the anonymous block it is called local
procedure
• This procedure doesn’t store in database and cannot be called outside anonymous
block
Parameters:
• This indicates that value must be supplied when you execute the procedure
• in , out , in/out
To view entire query of a procedure:
select * from user_source where name = ’P_first’;
Create Or Replace:
it would not affect grants which is given to objects and not affect the dependencies
select * from user_dependencies
create: completely clears the grams and dependencies
REF CURSOR:
Cursor→static
Ref cursor→ dynamic
• It is a data type
• It will close implicit
• entire table result output
• mostly give ref cursor to front end user
strong ref cursor:
• we know structure at compilation time
• it returns a value which can be of any data type
weak ref cursor:
• doesn’t know structure at compilation time
• query result will be stored](https://image.slidesharecdn.com/oraclequeans-210816121459/85/Paper-Presentation-of-SQL-and-PL-SQL-48-320.jpg)
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52
• Whatever declared in package specification is global.
• Subprogram which is defined in specification should be declared in body.
• we can compile only specification
Package body:
• it contains definitions
• it contained definition of subprogram that is listed in package specification
• it also contain the definition of subprogram that is listed in the package specification.
• It also contains local procedure it will be one time procedure it is also called as
private procedure.
• You can delete the package body without deleting the package specification.
Note:
• Subprogram which is defended package may or may not be present in specification.
• You can compile specification body by using
• We can compile body also.
Advantages:
• When package subprogram are executed for first time it is loaded to memory, further
execution of subprogram doesn’t require disk I/O.
• Packages supports Overloading concepts.
• Subprogram defend in package specification are global subprogram or global variable
in specification.
Overloading: [by using assign parameters]:
• P1 (difference in number of arguments)
• P2 (difference in parameter data type)
• P3(difference in their parameter name)
Grant execute on (pkg132 systems);
SQL query tuning:
• Select field instead of select *
• Avoid using select distinct
• Create join using with inner join [not using word]
• Use where instead of having for filter purpose
• use wild card operator at the end of phrase only (%)
• use limit to sample query result
• run your query during off peak hours
Pragma serially reusable:
• Memory allocation of constant
• Declaration in specification](https://image.slidesharecdn.com/oraclequeans-210816121459/85/Paper-Presentation-of-SQL-and-PL-SQL-52-320.jpg)
![53
53
Bodiless packages:
• You can use the bodiless packages for execution
• Here this variable exists only in this session
Performance tuning:
• First we will check for the date counts
• We will go For the table statistics which place primary role in performance tuning ( no
of rows in explain plan is based on status gathered]
• If not we use gathered status for all the table
• Then we will check for the index and make sure index are in valid state or not
• If not we will rebuild the index
Block level:
• for any block level tuning we will go for DBMS profiler (it’s getting ROWID and long
running SQLID then process goes for explain plan
• we also get AWR report from DBA Team getting SQL statistics information that is
(automated workload repository) from there we get long running SQL ID)
• then we take explain plan for the query
• From explain plan we get what type of scan it goes for
o Table full scan
o Index scan
o Index unique scan
o Index range scan
o Index full scan
o Index fast full scan
• Then we use the hints to change the optimizer plan
• We check up on the cardinality, costs and bytes like this performance tuning goes on.
PARTITION AND INDEX (ORACLE INDEX)::
TABLE PATITIONING:-
• Table partition is a method of splitting an object (table or index) into separate
partitions based on some criteria. The criteria can be date, number or character.
• If table contains more number of rows then queries takes more time to execute a query
and table becomes harder to manager. So in that case we use table partitioning to
overcome those issues. We can partition Table, Index & Materialized View.
• Partition allows table, index and index organized a table to be subdivided into smaller
pieces
• It is used to reduce the cost and improving performance of application.](https://image.slidesharecdn.com/oraclequeans-210816121459/85/Paper-Presentation-of-SQL-and-PL-SQL-53-320.jpg)
![61
61
UNIX:
Only lowercase character
Double click → copy
right click → paste
ctrl+c=cut the process
pwd→present working directory
cd demo →change directory
cd .. →previous directory
cd user/demo/change→ directly go to the directory
mkdir demo→ create directory
touch l.txt / touch l.pdf→create a file
Is→ print of list of files and sub directory
Is-a → hidden files also
Is*.txt→find only extension file that given
Is-lrt→find list of files with date and time
Find l.sql→find specified named file
Rm l.txt→delete a
Rm -r demo→delete a directory
Cp 2.pdf demo→copy a file to another directory
Cp-r→copy a directory to another directory
Cat 2.sql→open a file in code
Edit:
Vi l.txt→ edit a file
i→insert type the detail
wq→ write & quit
q→quit/view l.sql→ views in vi
tar-cvzf→zip the folder
tar-xvzf→unzip the folder
grep’demo’l.txt→word Finder [case sensitive]
grep-i’demo’l.txt→ word Finder [case insensitive]
sed’s/india/tamil/’→replace word/any string
sed’s/1/t/g/’→replace letters globally
Echo’prawin’→print
Prawin=10
Echo $ prawin print 10
Sed ‘5d’ l.txt→ delete the 5th
line
Sed ‘$d’ l.txt→ delete the last line
Sed ‘3,6d’ l.txt→ delete range of line
Chmod 777(user/group/others)
4-read(r)
2-write(w)
1-excute(x)
777- give all permissions to all users
651→read write /read execution/ execution](https://image.slidesharecdn.com/oraclequeans-210816121459/85/Paper-Presentation-of-SQL-and-PL-SQL-61-320.jpg)
![67
67
Column : also called this as columns, fields, attributes -1000 columns
Rows: also called this as rows records and tuple- no limit
Can we create a table to another table?
You can create one table from another by adding a SELECT statement at the end of
the CREATE TABLE statement:
CREATE TABLE new_tbl [AS] SELECT * FROM orig_tbl;
Insert into table of subquery (select)
Once we can create table based on another table constraints will copy to other table.
Can you able to join Nested table into D.B.?
Yes, you can join using Table ()
Why we use create or replace each time?
Grant permission of dependency object can not be revoked.
What is the difference between pre-select and pre-query?
A pre-query trigger fire before the query executes and fire once while you try to query. With
the help of this trigger you can modify the where clause part dynamically.
Pre-select query fires during the execute query and count query processing after Oracle
forms construct the select statement to be issued, but before the statement is actually issued.
Pre-query trigger fires before Pre-select trigger.
Explain character-manipulation functions? Explains its different types in SQL.
Character-manipulation functions are used to change, extract, and alter the character string.
When one or more characters and words are passed into the function, the function will
perform its operation on those input strings and return the result.
The following are the character manipulation functions in SQL:
A) CONCAT: This function is used to join two or more values together. It always appends
the second string into the end of the first string. For example:
Input: SELECT CONCAT ('Information-', 'technology') FROM DUAL;
Output: Information-technology
B) SUBSTR: It is used to return the portion of the string from a specified start point to an
endpoint. For example:
Input: SELECT SUBSTR ('Database Management System', 9, 11) FROM DUAL;
Output: Management
C) LENGTH: This function returns the string's length in numerical value, including the
blank spaces. For example:
Input: SELECT LENGTH ('Hello Javatpoint') FROM DUAL;
Output: 16
D) INSTR: This function finds the exact numeric position of a specified character or word in
a given string. For example:
Input: SELECT INSTR ('Hello Javatpoint', 'Javatpoint');
Output: 7](https://image.slidesharecdn.com/oraclequeans-210816121459/85/Paper-Presentation-of-SQL-and-PL-SQL-67-320.jpg)
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How to execute a stored procedure?
There are two way to execute a stored procedure.
From the SQL prompt, write EXECUTE or EXEC followed by procedure_name.
1. EXECUTE or [EXEC] procedure_name;
Simply use the procedure name
1. procedure_name;
What are the advantages of stored procedure?
Modularity, extensibility, reusability, Maintainability and one time compilation.
What is the difference between syntax error and runtime error?
A syntax error can be easily detected by a PL/SQL compiler. For example: incorrect spelling
etc. while, a runtime error is handled with the help of exception-handling section in a
PL/SQL block. For example: SELECT INTO statement, which does not return any rows.
Explain the Commit statement?
Following conditions are true for the Commit statement:
o Other users can see the data changes made by the transaction.
o The locks acquired by the transaction are released.
o The work done by the transaction becomes permanent.
What is mutating table error?
Mutating table error is occurred when a trigger tries to update a row that it is currently using.
It is fixed by using views or temporary tables.
What is consistency?
Consistency simply means that each user sees the consistent view of the data.
Consider an example: there are two users A and B. A transfers money to B's account. Here
the changes are updated in A's account (debit) but until it will be updated to B's account
(credit), till then other users can't see the debit of A's account. After the debit of A and credit
of B, one can see the updates. That?s consistency.
What is cursor and why it is required?
A cursor is a temporary work area created in a system memory when an SQL statement is
executed.
A cursor contains information on a select statement and the row of data accessed by it. This
temporary work area stores the data retrieved from the database and manipulate this data. A
cursor can hold more than one row, but can process only one row at a time. Cursor are
required to process rows individually for queries.](https://image.slidesharecdn.com/oraclequeans-210816121459/85/Paper-Presentation-of-SQL-and-PL-SQL-74-320.jpg)
Paper Presentation of SQL and PL/SQL
- 1. 1 1 CONTENTS INTRODUCTION: DML, DDL,DCL&TCL.................................................................................................2 JOINS:.............................................................................................................................................................13 AGGREGATE: ..............................................................................................................................................17 ANALTICAL: ................................................................................................................................................19 SET OPERATORS:.......................................................................................................................................20 STRING:.........................................................................................................................................................23 CASE & DECODE: .......................................................................................................................................24 NULL HANDLING: ......................................................................................................................................25 SYSNONMYS: ...............................................................................................................................................26 SEQUENCE: ..................................................................................................................................................27 CONSTRAIN: ................................................................................................................................................28 VIEWS & MATERIALIZED VIEW:..........................................................................................................31 INDEX: ...........................................................................................................................................................34 GTT:................................................................................................................................................................38 SUB QUERYS & PIVOT:.............................................................................................................................39 PL/SQL: ..........................................................................................................................................................41 PERFORMANCE TUNING:........................................................................................................................41 ANONYMOUS & CURSOR BLOCK:........................................................................................................43 COLLECTIONS:...........................................................................................................................................44 PROCEDURES:.............................................................................................................................................47 REF CURSOR: ..............................................................................................................................................48 EXCEPTIONS: ..............................................................................................................................................49 FUNCTIONS:.................................................................................................................................................50 PACKAGES: ..................................................................................................................................................51 PARTITION AND INDEX (ORACLE INDEX):: ......................................................................................53 TRIGGER: .....................................................................................................................................................56 HINTS AND TABLE REGONIZATION:...................................................................................................58 NORMALIZATION:.....................................................................................................................................60 OTHER QUESTIONS:..................................................................................................................................61 UNIX: ..............................................................................................................................................................61
- 2. 2 2 INTRODUCTION: DML, DDL,DCL&TCL In which language Oracle has been developed? Oracle has been developed forton and redone by C Language. What are the components of logical database structure in Oracle database? Components of logical database structure. Tablespaces Database's schema object What is a tablespace? A database contains Logical Storage Unit called tablespaces. A tablespace is a set of related logical structures. Actually a tablespace groups related logical structures together What is SQL? SQL stands for the Structured Query Language. SQL is a standard query language used for maintaining the relational database and perform many different operations of data manipulation on the data. SQL initially was invented in 1970. It is a database language used for database creation, deletion, fetching rows and modifying rows, etc. sometimes it is pronounced as 'sequel. What are the subsets of SQL? Data definition language (DDL):DDL is used to define the data structure it consists of the commands like CREATE, ALTER, DROP, etc. Data manipulation language (DML):DML is used to manipulate already existing data in the database. The commands in this category are SELECT, UPDATE, INSERT, etc. Data control language (DCL):DCL is used to control access to data in the database and includes commands such as GRANT, REVOKE. Transaction Control Language(TCL): it is used to validate tha transaction such as commit, rollback What is a Data Definition Language? Data definition language (DDL) is the subset of the database which defines the data structure of the database in the initial stage when the database is about to be created. It consists of the following commands: CREATE, ALTER and DELETE database objects such as schema, tables, view, sequence, etc.
- 3. 3 3 What is a Data Manipulation Language? Data manipulation language makes the user able to retrieve and manipulate data. It is used to perform the following operations. Insert data into database through INSERT command. Retrieve data from the database through SELECT command. Update data in the database through UPDATE command. Delete data from the database through DELETE command. What is Data Control Language? Data control language allows you to control access to the database. DCL is the only subset of the database which decides that what part of the database should be accessed by which user at what point of time. It includes two commands GRANT and REVOKE. GRANT: to grant the specific user to perform a particular task REVOKE: to cancel previously denied or granted permissions. What are privileges and Grants? Privileges are the rights to execute SQL statements – means Right to connect and connect. Grants are given to the object so that objects can be accessed accordingly. Grants can be provided by the owner or creator of an object. SET TRANSACTION? → It is used to set current transaction to read only and read write. → This doesn't affects other transaction by other users. → To end this transaction use ‘COMMIT’ or ‘ROLLBACK’. → Name is the transaction name given by user. Example 1 :- SET TRANSACTION READ ONLY NAME 'TORENTO'; Example 2 :- SET TRANSACTION READ WRITE NAME 'TORENTO'; Difference between varchar and varchar2 data types? Varchar can store upto 2000 bytes and varchar2 can store upto 4000 bytes. Varchar will occupy space for NULL values and Varchar2 will not occupy any space. Both are differed with respect to space. What is BLOB datatype? A BLOB data type is a varying length binary string which is used to store two gigabytes memory. Length should be specified in Bytes for BLOB. What is RAW datatype? RAW datatype is used to store values in binary data format. The maximum size for a raw in a table in 32767 bytes.
- 4. 4 4 What are the components of database structure in oracle? ANS: There are two type of database component physical database structure & logical database structure. What are the components of physical database structure of Oracle database? Oracle database is comprised of three types of files. One or more data files, two are more redo log files, and one or more control files. What is Physical database structure? ANS: Physical database structure of oracle database are control files, redo log files and datafiles. Datafile: This component stores the actual data. Each datafile is associated with only one database and tablespace. Redo Log files: These are more or less like backup files which are written before any changes to data files are written. Control files: These files contain the database structure information. Information like database creation date, name, redo threads, archive log history etc is stored. What is Logical database structure? ANS: Logical database structure includes tablespaces, schema objects, data blocks, extents and segments. Tablespaces Database is logically divided into one or more tablespaces. Each tablespace creates one or more datafiles to physically store data. Schema objects Schema objects are the structure that represents database's data. Schema objects include structures such as tables, views, sequences, stored procedures, indexes, synonyms, clusters and database links. Data Blocks Data block represents specific number of bytes of physical database space on disk. Extents An extent represents continuous data blocks that are used to store specific data information. Segments A segment is a set of extents allocated for a certain logical structure.
- 5. 5 5 What is table lock? ANS: Table lock prevents conflicting DDL operations that would override data changes in a current transaction. Table Locks (TM) A transaction automatically acquires a table lock (TM lock) when a table is modified with the following statements: INSERT , UPDATE , DELETE , MERGE , and SELECT ... FOR UPDATE . These DML operations require table locks to reserve DML access to the table on behalf of a transaction and to prevent DDL operations that would conflict with the transaction. Types of Table Lock? ANS: There are five different types of locks in Oracle, and they are: exclusive, shared, shared row exclusive, row shared, and row exclusive. How to remove Table Lock? ANS: You can release the lock using ROLLBACK or COMMIT. The DISABLE TABLE LOCK only prevents DDL operations to be performed (like ALTER TABLE, DROP TABLE, a.s.o. ), and PARALLEL DML, it DOES NOT prevent normal (serial) DML statements. What is meant by Deadlock Situation? ANS: It is a situation in which two or more transaction are waiting for data locked by each other, resulting in all sessions being blocked. Oracle automatically detects & resolves deadlock by rolling back the statement associated with transaction that detects deadlock. What is table Re-org? ANS: The main goal of table reorganization is to reduce IO when accessing the big database tables. 1. Reorders the table data according to the primary key index. 2. Column reordering to push columns that have no data, nulls, to the end of the table row The column reordering can be very useful for tables that have 300+ columns many of the columns are null. When the null columns are pushed to the end of the row, the read operation becomes streamlined thus increasing performance. What is Save point? ANS: It is a marker. It is used to identify a point to which you can roll back later. If two save point have same name then when you rollback will done until the last occurrence of the save point. OR Use the SAVEPOINT statement to identify a point in a transaction to which you can later roll back.
- 6. 6 6 How can we save images in database ? ANS: we can save image in D.B by using BLOB datatype. D.B. images are converted into BLOB, inserted in D.B then stored. What is database Dictionary? How it can be created? ANS: Data dictionary is a set of database tables used to store information about D.B. definition. It contains information about D.B. object such as Tables, Views, Indexes, Column, datatypes. To create data dictionary create connection to your D.B, then select connection, right click & choose generate DB Doc. How to edit VARCHAR2 Limit? ANS: Step1. ADD a column with any name/ dummy name with desired varchar limit Step2. Update all data from existing column to new dummy column Step3. Drop old Column Step4. Rename new column with old column name. What is Oracle table? A table is the basic unit of data storage in an Oracle database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns. What are Clusters? Clusters are groups of one or more tables physically stores together to share common columns and are often used together. What does ROLLBACK do? ROLLBACK retracts any of the changes resulting from the SQL statements in the transaction. What is the usage of SAVEPOINTS? SAVEPOINTS are used to subdivide a transaction into smaller parts. It enables rolling back part of a transaction. Maximum of five save points are allowed. Define transaction? A transaction is a sequence of SQL statements that Oracle Database treats as a single unit.
- 7. 7 7 What is the difference between sql & oracle? SQL is Stuctured Query Language.Oracle is a Database.SQL is used to write queries against Oracle DB. What are different Oracle database objects? TABLES VIEWS INDEXES SYNONYMS SEQUENCES TABLESPACES What is schema? A schema is collection of database objects of a user. What are Roles? Roles are named groups of related privileges that are granted to users or other roles. What are the dictionary tables used to monitor a database spaces ? DBA_FREE_SPACE DBA_SEGMENTS DBA_DATA_FILES What is a database instance? A database instance is a set of memory structure and background processes that access a set of database files. The processes can be shared by all of the users. What are parameters? Parameters provide a simple mechanism for defining and setting the valuesof inputs that are required by a form at startup.Form parameters are variables of type char,number,date that you define at design time. What are the different file extensions that are created by oracle reports? Rep file and Rdf file. 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.
- 8. 8 8 What is bind reference and how can it be created? Bind reference are used to replace the single value in sql, pl/sql statements a bind reference can be created using a (:) before a column or a parameter name. How many LONG columns are allowed in a table? Is it possible to use LONG columns in WHERE clause or ORDER BY? Only one LONG column is allowed. It is not possible to use LONG column in WHERE or ORDER BY clause. What is BCP? When does it used? BulkCopy is a tool used to copy huge amount of data from tables and views. BCP does not copy the structures same as source to destination. What is SYSTEM tablespace and when is it created? Every Oracle database contains a tablespace named SYSTEM, which is automatically created when the database is created. The SYSTEM tablespace always contains the data dictionary tables for the entire database. Which date function returns number value? months_between What is the default return value of a function? The default return value from a function is int. In other words, unless explicitly specified the default return value by compiler would be integer value from function. What is the difference between oracle, sql and sql server? Oracle is based on RDBMS. SQL is Structured Query Language. SQL Server is another tool for RDBMS provided by MicroSoft. What is SGA? The System Global Area in an Oracle database is the area in memory to facilitate the transfer of information between users. It holds the most recently requested structural 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 pool area. 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.
- 9. 9 9 What is dual? Dual is a dummy table and it contains only one columns. What is the data type of DUAL table? The DUAL table is a one-column table present in oracle database. The table has a single VARCHAR2(1) column called DUMMY which has a value of 'X'. How do we display rows from the table without duplicates? Duplicate rows can be removed by using the keyword DISTINCT in the select statement. What is the fastest query method to fetch data from the table? Row can be fetched from table by using ROWID. Using ROW ID is the fastest query method to fetch data from the table. What is Data Dictionary Table? It is a Meta data about the data base Difference between Delete and Truncate? DELETE TRUNCATE • We can Rollback after delete. • No tablespace is reduced We can't Rollback after performing Truncate. Tablespace is reduced (ii) Delete does not reset identity of table. (ii). Truncate reset identity of table. Data stored in low level watermark Data stored in high level watermark Implicit commit Auto commit (iii) It locks the table row (Row Level Lock). (iii). It locks the entire table (Table Level Lock) (iv) Its DML(Data Manipulation Language) command. (iv) Its DDL(Data Definition Language) command. (v) We can use WHERE to filter data to delete. (v) We can't use WHERE clause with it. (vi) Trigger is fired. (vi) Trigger is not fired while truncate. (vii) Syntax : DELETE FROM table_name ; DELETE FROM table_name WHERE example_column_id IN (1,2,3) ; (vii) Syntax : 1) TRUNCATE TABLE table_name;
- 10. 10 10 Blob Clob The full form of Blob is Binary Large Object. The full form of Clob is Character Large Object. This is used to store large binary data. This is used to store large textual data. This stores values in the form of binary streams. This stores values in the form of character streams. Using this you can store files like text files, PDF documents, word documents etc. Using this you can stores files like videos, images, gifs, and audio files. COMMIT ROLLBACK (i) COMMIT validates the modifications made by the current transaction. (i) ROLLBACK erases the modifications made by the current transaction. (ii) After execution of COMMIT statement, the transaction can not be ROLLBACK. (ii) Once ROLLBACK is executed database reaches its previous state, I.e. before the execution of the first statement of the transaction. (iii) COMMIT occurs when the transaction gets executed successfully. (iii) ROLLBACK occurs when the transaction is aborted in middle of the execution. (iv) Syntax :- COMMIT; (iv) Syntax :- ROLLBACK; ROWID ROWNUM (i) ROWID is nothing but Physical memory allocation. (i) ROWNUM is nothing but the sequence which is allocated to that data retrieval bunch. (ii) ROWID is permanent to that row which identifies the address of that row. (ii) ROWNUM is temporarily allocated sequence to the rows. (iii) ROWID is 16 digit Hexadecimal number which is uniquely identifies the rows. (iii) ROWNUM is numeric sequence number allocated to that row temporarily. (iv) ROWID returns PHYSICAL ADDRESS of that row. (iv) ROWNUM returns the sequence number to that row. (v) ROWID is automatically generated unique id of a row and it is generated at the time of insertion of row. (v) ROWNUM is an dynamic value automatically retrieved along with select statement output. (vi) ROWID is the fastest means of accessing data. (vi) ROWNUM is not related to access of data.
- 11. 11 11 Difference between Delete Truncate and Drop? DELETE TRUNCATE DROP Deletes some or all rows of a table Deletes all rows of a table Removes all rows and also the table definition, including indexes, triggers, grants, parameters DML DDL DDL Commit required Commit not required Commit not required Uncommitted deletes can be rolled back Cannot be rolled back – once truncated, gone forever A dropped table can be reinstated from the recycle bin Filter criteria be specified via WHERE clause No filter criteria allowed, removes all rows No filter criteria allowed, removes all rows DELETE triggers fired No triggers fired No triggers fired DELETE can be slow especially if the table has many triggers, indexes, and other dependencies TRUNCATE is fast for deleting all rows, even more than dropping and recreating the table using DROP DROP may not be as fast as TRUNCATE, as dropping and re-creating the table requires you to re-grant object privileges, re-create indexes, constraints, etc. DELETE ANY TABLE allows you to delete rows from any table of any schema. DROP ANY TABLE system privilege. DROP ANY TABLE system privilege. DELETE privilege on a specific table can be granted to another user or role. TRUNCATE privilege on a specific table cannot be granted to another user or role. DROP ANY privilege on a specific table cannot be granted to another user or role. CHAR VARCHAR CHAR stores fixed length character string VARCHAR stores variable length character strings String length is between 1-2000 String length is between 1-4000 It can hold max 256 character It can hold max 65,535 character It uses static memory allocations It uses dynamic memory allocations It is 50% faster than VARCHAR It is slower than CHAR VARCHAR VARCHAR2 VARCHAR can store up to 2000 bytes. VARCHAR2 can store up to 4000 bytes of characters. If we declare datatype as VARCHAR then it will occupy space for NULL values. In the case of VARCHAR2 datatype, it will not occupy any space for NULL values.
- 12. 12 12 What is ROWID? ROWID is a pseudo column attached to each row of a table. It is 18 characters long, blockno, row number are the components of ROWID. What is an alias in SQL statements? Alias is a user-defined alternative name given to the column or table. By default column, alias headings appear in upper case. Enclose the alias in double quotation marks (“ “) to make it case-sensitive. “AS” Keyword before the alias name makes the SELECT clause easier to read. For example Select emp_name AS name from employee; (Here AS is a keyword and “name” is an alias). How a SQL Query run? FROM WHERE JOINS GROUP BY HAVING SELECT ORDER BY LIMIT Difference between OLTP & OLAP? OLTP OLAP It is an online transactional system and manages database modification. It is an online data retrieving and data analysis system. Insert, Update, Delete information from the database. Extract data for analyzing that helps in decision making. OLTP and its transactions are the original source of data. Different OLTPs database becomes the source of data for OLAP. OLTP has short transactions. OLAP has long transactions. The processing time of a transaction is comparatively less in OLTP. The processing time of a transaction is comparatively more in OLAP. Simpler queries. Complex queries. Tables in OLTP database are normalized (3NF). Tables in OLAP database are not normalized. OLTP database must maintain data integrity constraint. OLAP database does not get frequently modified. Hence, data integrity is not affected.
- 13. 13 13 JOINS: What is the usage of Merge Statement? Merge statement is used to select rows from one or more data source for updating and insertion into a table or a view. It is used to combine multiple operations. Equi join will omit null values, Outer Join will not omit null values. Equi Join T1 T2 1 1 T1 T2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3 X 2 = 6 RECORDS 1 1 1 NULL 1 1 1 1 1 1 1 1 1 1 1 1 NULL NULL 1 1 1 1 1 1 NULL ONLY TABLE STRUCTURE On & And The Filtered Records Will Be Displayed As Null On & Where The Filtered Records Will Be Flushed Out Which are the most commonly used SQL joins? Most commonly used SQL joins are INNER JOIN and LEFT OUTER JOIN and RIGHT OUTER JOIN. What are the different types of joins in SQL? Joins are used to merge two tables or retrieve data from tables. It depends on the relationship between tables. Following are the most commonly used joins in SQL: Inner Join: inner joins Outer Join: outer joins are of three type: right outer join Left outer join Full outer join
- 14. 14 14 What is Inner Join in SQL? Inner join: INNER JOIN OR EQUI JOIN • To select matched rows from two or more table is called equi join. • It can be called as inner join or natural join (natural join find common columns from both the table). INNER JOIN What is Right Join in SQL? Right Join: RIGHT OUTER JOIN To get matched record from both the table and unmatched record from right table. RIGHT JOIN What is Left Join in SQL? Left Outer Join To get matched record from both the table and unmatched record from left table. LEFT JOIN What is Full Join in SQL?
- 15. 15 15 Full Join: FULL OUTER JOIN To get both matched and unmatched record from both the table. FULL OUTER JOIN What is self-join and what is the requirement of self-join? A self-join is often very useful to convert a hierarchical structure to a flat structure. It is used to join a table to itself as like if that is the second table How to fetch the unmatched records? Use FULL OUTER JOIN Then, use WHERE clause to filter only null values. How to fetch common records? Use INTERSECT – Fetch Common records from two columns Use INNER JOIN – Fetch Common records from two tables What is Cartesian product or cross-join? ANS: The Cartesian product, also referred to as a cross-join, returns all the rows in all the tables listed in the query. Each row in the first table is paired with all the rows in the second table. CROSS JOIN It is a Cartesian product. Number of rows in first table is joined with number of rows in the second table. Cartesian product is formed when user ignores ‘WHERE’ clause. Cross join is used by developers to perform performance testing.
- 16. 16 16 SEMI JOIN? → It returns row from first table when one or more row matched found in second table. → → Difference between semi-join and inner join is that row in first table will be returned only once even if the second table contains two matches from a row in the first table, only one copy of the row will be returned. → Semi-joins are written by using ‘IN’ & ‘EXISTS’ constructs. ANTI JOIN? → It returns row from first table when no matches found in second table. → Anti-joins are written by using ‘NOT IN’ & ‘NOT EXISTS’ constructs. Difference between Inner, Left outer, Right outer and Full outer joins? Inner Join Or Simple Join Left Outer Join Right Outer Join Full Outer Join Inner joins join the multiple tables and return those rows for which the join condition is true. The inner join is the most common join among the types of join. The Left Outer Join returns contain all rows from the LEFT table ( according to the specified in ON condition) and from the other table only those rows where the joined condition is true. The RIGHT OUTER JOIN returns contain all rows from the RIGHT table (according to the specified in ON condition) and from the other table only those rows where the joined condition is true. The Full Outer Join returns contain all rows from the LEFT table and RIGHT table with null in fields where the join condition is not true. SELECT column [ , column ] FROM t1 INNER JOIN t2 ON t1.column = t2.column; SELECT column [ , column ] FROM t1 LEFT [OUTER] JOIN t2 ON t1.column = t2.column; SELECT column [ , column ] FROM t1 RIGHT [OUTER] JOIN t2 ON t1.column = t2.column; SELECT column [ , column ] FROM t1 FULL [OUTER] JOIN t2 ON t1.column = t2.column; The Oracle INNER JOIN returns the intersect records of t1 and t2 as a result. The Oracle LEFT OUTER JOIN returns all the records from t1 and the intersect records of t1 and t2 as a result. The Oracle RIGHT OUTER JOIN returns all the records from t2 and the intersect records of t1 and t2 as a result. The Oracle FULL OUTER JOIN returns all the records from t1 and t2 tables as a result.
- 17. 17 17 How can you fetch common data from 2 column? ANS: we can fetch common data from two column by using Intersect or inner join depending upon what actually you mean by common data. Difference between Equi join & Outer join? Equi Joins Outer Joins Oracle Equi Joins retrieves the matching column values of the multiple tables. The join condition or the comparison operator present in the WHERE clause of the select statement. Another type of joins is an outer join which returns a result of an inner join plus all the rows from one table for which the join condition is not true. SELECT column [ , column ] FROM t1 , t2 where t1.column = t2.column; SELECT column [ , column ] FROM t1 LEFT | RIGHT | FULL [OUTER] JOIN t2 ON t1.column = t2.column; The Oracle Equijoin returns the intersect records of t1 and t2 as a result. There are three types of outer join as given below: Left Outer Joins (also called as Left Joins) Right Outer Joins (also called as Right Joins) Full Outer Joins (also called as Full Joins) AGGREGATE: Count(*),Count(Coulmn) Will Be 0 If No Records But Max , Min Values Is Null COUNT(COLUMN_NAME) COUNT(*) Counts the entries in a column - ignoring null values. Counts the rows in table - including null values. Both are aggregate function or group function. Both are aggregate function or group function. Count(1) Count(*) Counts The Rows In Table - Including Null Values. Counts The Rows In Table - Including Null Values. Counts Row By accessing An Index Counts Row Produced By Query Fast, because it access index SLOW Oracle Property ANSII standard
- 18. 18 18 GROUP BY ORDER BY Performs Grouping function Performs sorting function Order of Column make no differences Order of Column make differences Group by clause is always placed before order by clause order by clause is always placed after group by clause Attribute under Aggregate function cannot be in Group By clause. Attribute under aggregate can be in Order By Clause. WHERE HAVING Used to filter records from tables Used to filter records from groups Act as a Pre-filter Act as a Post-filter Used without group by clause Must use group by clause SELECT and other statements such as UPDATE, DELETE or either one of them. Can't be used without a SELECT statement. GROUP BY comes after WHERE GROUP BY comes before HAVING. (i) Implemented in row operations. (i) Implemented in column operations. (ii) Applied to Single row. (ii) Applied to summarized row or groups. When do you use WHERE clause and when do you use HAVING clause? The WHERE condition lets you restrict the rows selected to those that satisfy one or more conditions. Use the HAVING clause to restrict the groups of returned rows to those groups for which the specified condition is TRUE. WHAT IS LISTTAGG() AGGREGATE?SEQ It is used to display records in a single array format by specific delimiter. STAGG() function is an aggregation function that transforms data from multiple rows into a single list of values separated by a specified delimiter. AGGREGATE FUNCTION ANALYTICAL FUNCTION It is used to give cumulative set of data It is used to give analysis set of data Column present in select should be present in group by clause Column present in select may or may not be present in group by clause We can group data by group by clause & filter by having clause We can group data by using partition keyword Single row output Multiple row output It will return single value It will return more than one value slower than analytical function faster comparing aggregate function Here we use Sum, Avg, Count, Min, Max Here we use Rank, Dense_rank, Lead, Lag, Row_number, First_value
- 19. 19 19 RULES FOR AGGREGATE: • Group functions accept only one argument. • Group functions ignore null values including COUNT (*). • Whenever column is followed by group function or group function followed by column should have ‘group by’. • The group functions SUM & AVG only work in number and not in date and character. • The ‘*’ cannot be used except COUNT. • When you are restricting with group functions use ‘HAVING’ clause. ANALTICAL: What is Analytical Function? ANS: Analytic functions are the last set of operations performed in a query except for the final ORDER BY clause. Analytical function is Multi rows output. Here we use partition by keyword for grouping. It will return more than one value. All columns is specified by using partition clause. No row collapse and number of input is equal to the number of output. Oracle Analytic Functions RANK DENSE_RANK. LEAD. LAG. FIRST_VALUE. LAST_VALUE. NTH_VALUE. NTILE. Difference between RANK and DENSE_RANK? RANK DENSE RANK Both are analytical function Both are analytical function (i) Both are analytical function. Skip sequence (i) Both are analytical function. Doesn’t skip sequence If there is any repeated rank it will skip the next rank If there is any repeated rank it will not skip the next rank Example :- Rank 1 1 3 1 is repeated 2 times so It will skip the 2nd rank and it will print 3 as next rank Example :- Dense_Rank 1 1 2 It will not skip any values, It will print in the same order
- 20. 20 20 Difference between LEAD and LAG? LEAD LAG Both are analytical function Both are analytical function It will fetch the next value of current row It will fetch the previous value of current row Example :- Lead 10000 , 20000 20000 , 30000 30000 , null Example :- Lag 10000 , null 20000 , 10000 30000 , 20000 SET OPERATORS: What are the set operators in SQL? It is used to merge two or more queries Union, Union All, Intersect or Minus operators are the set operators used in the SQL. Difference b/w union and union all Union Union all Join 2 query by eliminate duplicates Only Merge 2 query Its sorting manner based on 1st column No sorting Slower compare to union all Faster compare to union Difference between Union And Union All Union Union All UNION: only keeps unique records UNION ALL: keeps all records, including duplicates It combines the result set from multiple tables and returns distinct records into a single result set. It combines the result set from multiple tables and returns all records into a single result set. Following is the basic syntax of UNION operator: SELECT column_list FROM table1 UNION SELECT column_list FROM table2; Following is the basic syntax of UNION ALL operator: SELECT column_list FROM table1 UNION ALL SELECT column_list FROM table2; It has a default feature to eliminate the duplicate rows from the output. It has no feature to eliminate the duplicate rows from the output. Its performance is slow because it takes time to find and then remove duplicate records. Its performance is fast because it does not eliminate the duplicate rows. Most database users prefer to use this operator. Most database users do not prefer to use this operator.
- 21. 21 21 Union All Full Outer Join Union is vertical - rows from table1 followed by rows from table2 (distinct for union, all for union all) & both table must have same number of columns with compatible datatypes. Full outer join is horizontal. Number of rows in full outer join is max of table1 and table 2 rows and number of columns = table1 columns + table2 columns. It is faster It is slower compared to Union all Intersect Minus Intersect Set operator is used to fetch the common records from 2 different tables . Minus Operator is used to fetch the records from first table which eliminates common records. It returns only the rows returned from both queries It returns unique rows selected by first query but not the rows selected from second query SELECT city_name FROM CUST_DATA INTERSECT SELECT city_name FROM SUPP_DATA; SELECT city_name FROM CUST_DATA MINUS SELECT city_name FROM SUPP_DATA; For Performance tuning Intersect operator is not preferable as it takes time to fetch duplicate records Minus operator is preferable operator in Performance tuning. What are the types of operators available in SQL? Operators are the special keywords or special characters reserved for performing particular operations and are used in the SQL queries. There is three type of operators used in SQL: Arithmetic operators: addition (+), subtraction (-), multiplication (*), division (/), etc. Logical operators: ALL, AND, ANY, ISNULL, EXISTS, BETWEEN, IN, LIKE, NOT, OR, UNIQUE. Comparison operator: =, !=, <>, <, >, <=, >=, !<, !> Rules of Set Operators? ANS: NUMBER OF COLUMNS IN SELECT CLAUSE SHOULD BE SAME. CORRESPONDING DATA TYPES SHOULD BE SAME. What are Wild card Operators? % and _ are wildcard operators % = Any number of Character _ = Escape Character It uses conjunction with ‘LIKE’ Operators.
- 22. 22 22 What is Wildcard Operator? ANS: The wildcard is an advanced search technique that can be used to maximize your search results in library databases. Wildcards are used in search terms to represent one or more other characters. What is Wildcard LIKE operator? ANS: The Oracle LIKE condition allows wildcards to be used in the WHERE clause of a SELECT, INSERT, UPDATE, or DELETE statement. This allows you to perform pattern matching. IN EXISTS The answer of IN can be TRUE or FALSE or NULL The answer of EXISTS can be TRUE or FALSE IN compares values between parent query and sub-query EXISTS cannot compare values between parent query and sub-query IN is used as multiple OR operator It can be used to determine if any values are returned or not IN is faster than EXISTS if sub-query result is less EXISTS is faster than IN if sub-query result is large NULL cannot be compared using IN condition NULL can be compared using EXISTS condition In operator test for the particular value in the sub query. Exist operator is a Boolean operator.so it works more efficient and faster than IN operator as it will be faster to process Boolean value rather than processing values itself. In operator scan all the values inside the IN block. EXISTS quit after 1st occurrence. In case of a big number of list from the select list IN operator should not be used. The exists shall be used with the proper condition this will definitely make the query optimal query. 'IN' can be used on sub-queries as well as with values. Whereas 'EXISTS' can only be used on sub-queries. IN picks the list of matching values. EXISTS returns the Boolean values like true or false. Exists is faster than in.
- 23. 23 23 The two most commonly used wildcards are: An asterisk (*) may be used to specify any number of characters. It is typically used at the end of a root word, when it is referred to as "truncation." This is great when you want to search for variable endings of a root word. For example: searching for educat* would tell the database to look for all possible endings to that root. Results will include educate, educated, education, educational or educator. A question mark (?) may be used to represent a single character, anywhere in the word. It is most useful when there are variable spellings for a word, and you want to search for all variants at once. For example, searching for colo?r would return both color and colour. STRING: Difference between Replace and Translate? REPLACE TRANSALATE it will replace set of string with another set of string It will replace set of string with another set of string by individual character. (i) Replaces entire string at a time. (i) Replaces character one-to-one basis. (ii) Returns string if no match found. (ii) Returns null if no match found. (iii) Syntax :- Replace ('Oracle','Ora',123 ) (iii) Syntax:- Translate ('Oracle','Oae',123 ) India Will Replace 123 Will Then Check Exact Match Of Ind Translate Replace 123 Will Then It Will Check By With Individual Character I Will Be Replaced By 1 N Will Be Replaced By 2 D Will Be Replaced By 3 What is difference between SUBSTR and INSTR? INSTR function search string for sub-string and returns an integer indicating the position of the character in string that is the first character of this occurrence.SUBSTR function return a portion of string, beginning at character position, substring_length characters long.SUBSTR calculates lengths using characters as defined by the input character set.
- 24. 24 24 Difference between INSTR and SUBSTR? INSTR SUBSTR (i) The INSTR function provides character position in a pattern of string. (i) The SUBSTR function returns a specific portion of a string. ii) INSTR is used to find the position of any particular character in a word which returns numeric value. (ii) SUBSTR is used to extract a set of characters from a string by specifying the character starting position and end position and length of characters to be fetched. (iii) INSTR returns numeric. (iii) SUBSTR returns string. WE USE 4 ARGUMENTS WE USE 3 ARGUMENTS (iv) Syntax :- INSTR('HELLO','E',1,2) (iv) Syntax :- SUBSTR('HELLO',2,3) CASE & DECODE: CASE DECODE Case will handle all type of relational operators like =,<=,>=,<> Decode will handle only equality check Case is a statement Decode is a function Null handling capability of case & decode is different Ex: null = null then 1 else 0 case will return 0. Because null is not equal to another null Ex: null = null then 1 else 0 decode will return 1. Because null is equal to another null (i) Complies with ANSII SQL (i) Oracle proprietary. (iv) Needs data consistency. (iv) Data consistency no needed. (v) NULL = NULL, returns FALSE (v) NULL = NULL, returns TRUE (vi) Can be used in PL/SQL block and SQL statements. (vi) Can be used in SQL Statements. (vii) Can be Used in parameters while calling a procedure. (vii) Cannot be Used in parameters while calling a procedure. What is DECODE function used for? DECODE is used to decode a CHAR or VARCHAR2 or NUMBER into any of several different character strings or numbers based on value. That is DECODE does a value-by-value substitution.
- 25. 25 25 NULL HANDLING: What is null value? Null Value is neither zero nor it is a blank space. It is some unknown value which occupies 4 bytes of space of memory in SQL. NULL:-??? • Null is a unassigned value or unknown value or undefined value. • Null is not equal to zero. • Null is not equal to space. • Null is not equal to underscore. • Null is not equal to Null. • Null is not equal to ‘’ Null is always greater than any number because in ascending order Null comes last and in descending order it comes first or it is maximum in ascending order & minimum in descending order. Describe different types of null handling Function used in SQL? NVL: Converts a null value to an actual value. NVL (exp1, exp2) .If exp1 is null then the NVL function returns the value of exp2. Replace null value NVL2: If exp1 is not null, nvl2 returns exp2, if exp1 is null, nvl2 returns exp3. The argument exp1 can have any data type. NVL2 (exp1, exp2, exp3) Replace both null value and not null value NULLIF: Compares two expressions and returns null if they are equal or the first expression if they are not equal. NULLIF (exp1, exp2) Null null – null 10 10 – null 10 null -10 Null 10- null COALESCE: Returns the first non-null expression in the expression list. COALESCE (exp1, exp2… expn). The advantage of the COALESCE function over the NVL function is that the COALESCE function can take multiple alternative values. Return the first not null value Define NULL? ANS: Null is an Unknown Undefined values. Null is not equal to zero(space/empty character). Null is not equal to another null.
- 26. 26 26 What is difference b/w nvl and nvl2 and coalesce? NVL NVL2 COALESCE (i) 2 arguments. (i) 3 arguments. (I) 2 or more arguments. (ii) If the first argument is null then display the second argument else display the first argument. (ii) If the first argument is null then display the third argument else display the second argument. (ii) It returns the first not null able column from the arguments list. (iii) Syntax :- NVL(1,2) (iii) Syntax :- NVL2(1,2,3) (iii) Syntax :- COALESCE(1,2) SYSNONMYS: What is synonym? A synonym is an alternative name for DATABASE or oracle object such as tables, view, sequences, stored procedures and other database objects. You can create synonym for synonym. Because it is a object of database. TYPES :- Private Synonym. (WITHIN SCHEMA) This synonym is accessed within the schema. The default one is private Public Synonym. (ACCESSED ACROSS or between THE SCHEMA) This synonym is accessed across or between the schema. Difference between a view and a synonym Synonym View Synonym is just a second name of table used for multiple link of database. synonym can be on view. View can be created with many tables, and with virtual columns and with conditions. What is the difference between a view and a synonym? Synonym is just a second name of table used for multiple link of database. View can be created with many tables, and with virtual columns and with conditions. But synonym can be on view.
- 27. 27 27 SEQUENCE: WHAT IS SQUENCE? • It unique auto generated number. • It has start with, increment by, min value, max value, cycle, cache. • Commit, save point or rollback doesn't work. • It is mainly used for generating primary key column values. • We cannot change start with in sequence. • Sequence can be shared with multiple tables. • Sequence sometimes act as primary key • It is a schema object. A sequence is an object in Oracle that is used to generate a number sequence. This can be useful when you need to create a unique number to act as a primary key. NUMBER GENERATOR AND SEQUENCE CAN NOT BE ROLLED BACK SEQUENCE CAN BE SHARED WITH MULTIPLE TABLES; CREATE SEQUENCE SEQ1 START WITH 1 INCREMENT BY 1 MINVALUE 1 MAXVALUE 10 NOCACHE NOCYCLE; Increment by: • Interval between sequence number • Either + or - value but not zero • (+)- ASC/(-)DESC • If you omit, then default (one) Max value: • It must be greater than equal to start with • Must be greater than min value Min value: • Must be lesser than equal to start with. • Must be lesser than Max value Start with: • Specify first sequence number to be generated.
- 28. 28 28 Cycle No cycle Cache No cache It specifies when sequence contain to generate when it is reached max / min well Default one this cycle not mentioned • Faster retrieval • Min=2 • Value of sea is pre- allocated Max= maxvalue- minvalue Default: cache 20. Value of sea is not pre-allocated Disadvantage of cache: Lost of sequence value if the system sudden a crash occurs. CONSTRAIN: Constraints are of two types. They are 1. Table Level Constraints :- The constraints can be specified after all the columns are defined. This is called table-level definition. 2. Column Level Constraints :- The constraints can be specified immediately after the column definition. This is called column-level definition. What is a primary key? • It is a unique identifier. • Ignores null values. • It is entity integrity. • It will not accept duplicate values. • It is a cluster index. • Only one primary key is allowed in a table. • If need more than one primary key its possible in composite primary key. • It automatically generates unique index. A primary key is a field or the combination of fields which uniquely specify a row. The Primary key is a special kind of unique key. Primary key values cannot be NULL. For example, the Social Security Number can be treated as the primary key for any individual. COMPOSITE PRIMARY KEY (P)? Usually table have only one primary key but if we want to set more than one primary key then we go for composite primary key.
- 29. 29 29 What is a foreign key? Foreign key is a key used to link two tables together. foreign key is field or a collection of field in one table that refers to the primary key in another table. Table containing foreign key is called child table. Table containing candidate key is called the reference or parent table. • It is Referential Integrity (RI). • It refers a primary (or) unique constraint of another table. • It accepts null values in child records. • It accepts duplicate values in child records. • It is like a parent and child relationship. A foreign key is specified as a key which is related to the primary key of another table. A relationship needs to be created between two tables by referencing foreign key with the primary key of another table. Foreign key acts like a cross-reference between tables as it refers to the primary key of other table and the primary key-foreign key relationship is a very crucial relationship as it maintains the ACID properties of database sometimes. Integrity constraint violation : child record found- delete. parent record not found -insert. On delete cascade: It will delete parent record and corresponding child records also On delete set null: It will delete parent record and corresponding child record it’ll set null What is a unique key? • It is unique identifier. • It accepts null values and can accept more than 1 null value. • It is entity integrity. • It is non – cluster index. • It automatically generates unique index. Unique key constraint uniquely identifies each record in the database. This key provides uniqueness for the column or set of columns. The Unique key cannot accept a duplicate value. The unique key can accept only on Null value. Not null key(C): It ignores null value. It is a domain integrity condition. Check [C]: It is a domain integrity It should satisfy your condition.
- 30. 30 30 Different between Primary key and Foreign key? Primary key Foreign key It is used to uniquely identify data in the table It is used to maintain relationship between tables It can’t be null It can accept the null values Two or more rows can’t have same primary key It can carry duplicate value for a foreign key attribute Primary has clustered index By default, It is not clustered index Primary key constraint can be defined on temporary table It can’t be defined on temporary tables Primary Key Unique key Used to serve as a unique identifier for each row in a table. Uniquely determines a row which isn’t primary key. Cannot accept NULL values. Can accept one NULL value. Only one primary key More than one unique key Creates clustered index Creates non-clustered index What is the difference between primary key and unique key? Primary key and unique key both are the essential constraints of the SQL, but there is a small difference between them Primary key carries unique value but the field of the primary key cannot be Null on the other hand unique key also carry unique value but it can have a single Null value field What is difference between UNIQUE constraint and PRIMARY KEY constraint? A column defined as UNIQUE can contain Nulls while a column defined as PRIMARY KEY can't contain Nulls. A table can have only one primary keys.
- 31. 31 31 VIEWS & MATERIALIZED VIEW: What is view in SQL ? 1 view is a virtual table. 2. It does not contain any physical data. 3. We can create view from another view. 4. Only queries stores in data dictionary table. Advantages of views? • To make more complex query look simple. Views Can Be Used To Reduce The Complexity Of The Database Schema Views Can Be Used As Mechanism To Implement Row And Column Level Security Views Can Be Used To Present Aggregated Data And Hide Detailed Data. • To restrict data access of views. What are the advantages of views? Provide an additional level of table security, by restricting access to a predetermined set of rows and columns of a table. Hide data complexity. Simplify commands for the user. Present the data in a different perspective from that of the base table Store complex queries What is materialized views Materialized view is a database objects that store the result of a query. It is a schema object. It can be called as snapshots. Materialized view occupies space in database. It will save the result set of the query in data dictionary table. We will not get updated data from Materialized view until we go for REFRESH Why use materialized view instead of a table? Materialized views are basically used to increase query performance since it contains results of a query. They should be used for reporting instead of a table for a faster execution. Advantages of materialized views: You can create materialized view on another materialized view. So that it reduces more network traffic. It can be either read only, writable or updatable. You can create materialized view for join queries and quires that contain aggregate functions. It reduces network traffic.
- 32. 32 32 Types of views 1. SIMPLE VIEW 2. COMPLEX VIEW 3. FORCE VIEW Difference between Simple view and Complex View? SIMPLE VIEW COMPLEX VIEW (i) Contains only one single base table or is created from only one table. (i) Contains more than one base tables or is created from more than one tables. (ii) We cannot use group functions like MAX(), COUNT(), etc. (ii) We can use group functions. (iii) Does not contain groups of data. (iii) It can contain groups of data. (iv) DML operations could be performed through a simple view. (iv) DML operations could not always be performed through a complex view. (v) INSERT, DELETE and UPDATE are directly possible on a simple view. (v) We cannot apply INSERT, DELETE and UPDATE on complex view directly. (vi) Simple view does not contain group by, distinct, pseudo column like ROWNUM, columns defined by expressions. (vi) It can contain group by, distinct, pseudo column like ROWNUM, columns defined by expressions. • It truncate & reload new data. • It is fast • Compare log file & fetch remaining data • It is slower Difference Complete, Fast and Force Refresh? Complete Refresh means you truncate entire materialized view and insert new data. Fast Refresh means you update (or insert/delete) only the rows which have been changed on master tables. And just as information Force Refresh mean, Oracle tries to make a Fast Refresh and if this is not possible then do Complete Refresh. Usually Fast Refresh is much faster than Complete Refresh but it has restrictions. You have to define MATERIALIZED VIEW LOG on master tables
- 33. 33 33 VIEW MATERIALIZED VIEW (i) A View is never stored it is only displayed. (i) A Materialized View is stored on the disk. (ii) View is the virtual table formed from one or more base tables or views. (ii) Materialized view is a SNAPSHOT physical copy of the base table. (iii) View is updated each time the virtual table (View) is used. (iii) Materialized View has to be updated manually or using triggers. (iv) Slow processing. (iv) Fast processing. (v) View do not require memory space. (v) Materialized View utilizes memory space. (vi) No need log file. (vi) It will maintain log files. (vii) Only select query has saved in data dictionary table. (vii) It will saves the output of the select query in data dictionary table. Types: simple, complex & force view Complete refresh , fast and force refresh (viii) Syntax :- Create View V As (viii) Syntax:- Create Materialized View V Build [clause] Refresh [clause] On [Trigger] As Without base table we can create table using force view Without base table we can not create MV Index can not be created in views Index can be created in MV Complete refresh Fast and force refresh It truncate and reload new data Compare log file fetch remaining data It is fast It is slow DBMS_MVIEWS.REFRESH(‘MV_1,’C’); DBMS_MVIEWS.REFRESH(‘MV_1,’F’); Force view: • Not an existent table. • No base table is necessary • We can create a view with the dummy based table which does not exist in the database. • This view will be having errors. • May be used for application code test.
- 34. 34 34 Manipulate data in view: Read only: This can be used where you don’t want to manipulate data in a view. Check option: This is used where you want to insert data in views by checking condition from where clause. Updateable: You can’t use order by and group by You can’t use analytical and aggregate function. How to Refresh View? ANS: To refresh the Oracle materialized view, call one of the procedures in DBMS_MVIEW. The DBMS_MVIEW package provides three types of refresh operations: DBMS_MVIEW. REFRESH: Refreshes one or more Oracle materialized views. MATERIALIZED VIEW LOG??? • Materialized view logs are used to track changes (insert, update and delete) to a table. • Purging materialized view logs. • It show no of changes made to a table. • If you refresh materialized view then this gets to zero. INDEX: INDEX is a database object. It plays key role in performance tuning. It is prefereable to create index on all varchar clause column in a query. It is used by the oracle server. It is based on rowid. Should be created when less of rows to be retrieved in a large table. It will effective if we Want to retrieve 4% of rows from the table. TYPES OF INDEX? B-TREE INDEX Balance tree index When We Have high cardinality(low duplicates it is preferable to create B-Tree index. Column that contains more than 100 unique records BITMAP INDEX When We Have low cardinality(high duplicates) it is preferable to create B-Tree index Column that contains less than 100 unique records FUNCTION BASED INDEX When We create index on functional based column it is functional index. It is not guaranteed that create functional index will be used all the time. Oracle optimizer will decide whether it should be used or not based on the cost effect.
- 35. 35 35 Trunc() column name Upper() column name What is an Index? An Index is an optional structure associated with a table to have direct access to rows, which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table. How you will avoid your query from using indexes? By changing the order of the columns that are used in the index, in the Where condition, or by concatenating the columns with some constant values. INDEX:- • It is used to improve the performance of query retrieval. • Index can be either Unique or Non-Unique index 1. UNIQUE INDEX : • It is created automatically when a user defines a primary/unique constraint for a column. 2. NON – UNIQUE INDEX : • Created by the user to speed up the retrieval of rows. • Maintained by oracle server WHEN TO CREATE INDEX :- • When a table is large. • When most of the queries are expected to retrieve less than 4% of rows from the table. • When a column contains a wide range of values. • When column is most often used as a condition in a query. • When a column contains large number of null values. WHEN NOT TO CREATE INDEX :- • When a table is small. • When most of the queries are excepted retrieve more than 4% of rows from the table. • When column contains a large number of duplicates. • When column is not most often used as condition in a query. • When a table is updated frequently.
- 36. 36 36 What is the unique Index? Unique Index: For creating a unique index, the user has to check the data in the column because the unique indexes are used when any column of the table has unique values. This indexing does not allow the field to have duplicate values if the column is unique indexed. A unique index can be applied automatically when a primary key is defined. What is Clustered Index in SQL? Clustered Index: The clustered index is used to reorder the physical order of the table and search based on the key values. Each table can have only one clustered index. The Clustered index is the only index which has been automatically created when the primary key is generated. If moderate data modification needed to be done in the table then clustered indexes are preferred. What is the Non-Clustered Index in SQL? Non-Clustered Index: The reason to create non-clustered index is searching the data. We well know that clustered indexes are created automatically primary keys are generated, but non-clustered indexes are created when multiple joins conditions and various filters are used in the query. Non- Clustered Index does not alter the physical order of the table and maintains logical order of data. Each table can have 999 non-clustered indexes. What is the difference between clustered and a non-clustered index? A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages. A Nonclustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk. What is Index • It is used to improve the performance of query retrieval. • Index can be either Unique or Non-Unique index What is UNIQUE INDEX : • It is created automatically when a user defines a primary/unique constraint for a column. What is NON – UNIQUE INDEX : • Created by the user to speed up the retrieval of rows. • Maintained by oracle server
- 37. 37 37 WHEN TO CREATE INDEX? • When a table is large. • When most of the queries are expected to retrieve less than 4% of rows from the table. • When a column contains a wide range of values. • When column is most often used as a condition in a query. • When a column contains large number of null values. WHEN NOT TO CREATE INDEX? • When a table is small. • When most of the queries are excepted retrieve more than 4% of rows from the table. • When column contains a large number of duplicates. • When column is not most often used as condition in a query. • When a table is updated frequently. Clustered Index Non-Clustered Index A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages. A Non-clustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk. B-Tree Index Bitmap Index Functional Index B-Tree index is an index that is created on columns that contain very unique values Bitmap is a method of indexing, offering performance benefits and storage savings Function-based indexes allow you to create an index based on a function or expression. B-Tree works best with many distinct indexed values Bitmap works best with many distinct indexed values CREATE INDEX idx_emp_id ON employee (id); CREATE BITMAP INDEX idx_emp_gender ON employee(gender); CREATE INDEX index_name ON table_name(function(column_name)); High Cardinality,Less Duplicates Low Cardinality, More Duplicates What is an Oracle index? An index is an optional structure associated with a table to have direct access to rows, which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table.
- 38. 38 38 What are the different index configurations a table can have? A table can have one of the following index configurations No indexes A clustered index A clustered index and many nonclustered indexes A nonclustered index Many nonclustered indexes. How to know which index a table is using? SELECT table_name,index_name FROM user_constraints. GTT: GLOBAL TEMPOARY TABLE:- • It is session level table. • It stores data only in session level once the session is close, all the data will be truncated or flushed out and only structure remains • It is used to store parameters values for the procedures • It is used to session level testing. • Data in temporary table is stored in temp segments in the temp table space. • Data in temporary tables is automatically deleted at the end of the database session, even if it ends abnormally. • Views can be created against temporary tables and combinations of temporary and permanent tables. • Temporary tables can have triggers associated with them. • Indexes can be created on temporary tables. The content of the index and the scope of the index is the same as the database session. TYPES :- → ON COMMIT PRESERVE ROWS This indicates that data should be present till the session ends. → ON COMMIT DELETE ROWS • This indicates that data should be deleted at the end of this transaction. • It is the default one. GTT WITH Clause (i) The main difference is that the temporary table is a stored table. (i) It will not saves in database. (ii) Views can create in GTT (ii) Views cannot create in WITH Clause. (iii) Index can be create in GTT (iii) Index cannot create in WITH Clause.
- 39. 39 39 Global temporary tables GTT Views Global temporary tables in Oracle are permanent database objects that store data on disk and visible to all sessions. An Oracle VIEW, in essence, is a virtual table that does not physically exist. Rather, it is created by a query joining one or more tables. PARSING :- Oracle needs to execute some task before executing SQL query (which is received from user). This process is called Parsing. 1. SYNTACTIC CHECK :- → Oracle parses the syntax to check for misspelled SQL keywords. 2. SEMANTIC CHECK :- → Oracle verifies all table names & column name from the data dictionary table and check to see if user is authorized to view data. 3. OPTIMIZATION :- → Oracle creates an execution plan on schema statistics. → If the entire above task performs then it is called hard parsing. → If only syntactic check & semantic check perform then it is called soft parsing. → Soft parsing occurs when you use ‘cursors’. SUB QUERYS & PIVOT: A query embedded within another query is called sub query. There are two types of sub query they are SINGLE ROW SUB QUERY When a sub query returns one row then it is called single row sub query. MULTI ROW SUB QUERY When a sub query returns more than one row is called multi row sub query. TYPES :- SCALAR SUB QUERY Whenever a ‘Select’ clause followed by sub query is called scalar sub query INLINE VIEW Whenever a ‘From’ clause followed by sub query is called Inline view or named sub query in a from clause is called Inline view.
- 40. 40 40 NESTED SUB QUERY Whenever a ‘Where’ clause followed by sub query is called nested sub query. Here first inner query is executed then outer query will be executed. It doesn’t have any reference between inner query and outer query. Inner query runs only once for outer query. CO-RELATED SUB QUERY When the inner query has reference to outer query is called correlated sub query. Here outer query runs first and then inner query is executed. It is user row by row processing. The inner query is executed once for every row of the outer query. It is faster. What are the various types of queries? The types of queries are : Normal Queries Sub Queries Co-related queries Nested queries Compound queries Nested Query Sub Query Correlated Query Sub Query In Nested Query, Inner query runs first, and only once. Outer query is executed with result from Inner query.Hence, Inner query is used in execution of Outer query. In Correlated Query, Outer query executes first and for every Outer query row Inner query is executed. Hence, Inner query uses values from Outer query. Bottom up approach i.e. Inner query runs first, and only once. Outer query is executed with result from Inner query. Top to Down Approach i.e. Outer query executes first and for every Outer query row Inner query is executed. Inner query execution is not dependent on Outer query. Inner query is dependent on Outer query. Performs better than Correlated Query but is slower than Join Operation. Performs slower than both Nested Query and Join operations as for every outer query inner query is executed. Difference between PIVOT and UNPIVOT and Reverse PIVOT PIVOT UNPIVOT Reverse PIVOT The PIVOT statement is used to convert table rows into columns The UNPIVOT operator converts columns back to rows. Reversing a PIVOT statement refers to the process of applying the UNPIVOT operator to the already PIVOTED dataset in order to retrieve the original dataset.
- 41. 41 41 PL/SQL: • Procedural language structured query language • It is a procedural language extension to SQL • SQL statement puts together in one single block and sends the entire block to the server in one single cell. • Thereby reducing network traffic. Benefits: • Performance benefit • Modularization→(large block of codes into smaller piece) • Portable • Exception handling • Programming features. SQL PLSQL It is a single query that is used to perform DML from DDL It is a block of codes used to write the entire program blocks Execute one statement at the time Executed as a block of code You can’t embed PLSQL in sql You can embed SQL in plsql It tells the database what to do It tells the database how to do things Interaction with database server No interaction with database server Used to manipulate data used to create an application C1%rowcount SQL%rowcount gives how many rows which will run Gives how many those affected in SQL query c-5 ex: 5rows table Sql-50 PERFORMANCE TUNING: • First we have to count all the dates Select count(1) from employees; • If increases in datacount, then we go for the “table stats” Select last_analyzed, T * from all_tables T Where Table_name = ‘emp_perF’ • Check for last analyzed will be in todays date otherwise Begin Dbms_statts.gather_table_stats(‘HR’,’emp_perF’) • Then we go for ‘explain plan’ Explain plan for Select E.ID, P_first_name from Employee E, Emp_perF P Where E.ID= P.employee_id; • Explained, then Select * from table(DBMS_XPLAN.DISPLAY());
- 42. 42 42 Explain Plan: • Always read from last /reverse • If the table contain number of bytes high and cost high go for that table. Operation in explain plan: Types of join : Hash Join(check =): • When we join large table with small table • Optimizer will create hash memory • Then, values of small tables stored in a hash memory • Hash memory created in large table only • Then go for equality check Nested loop Join: • Co-related query • When we have less no of results set • when join two large table Merge join: Other than equality check Oracle Optimizer: RBC-Rule based optimizer →(before 11g only RBC) CBC-Cost based optimizer BMC Remedy: • it is ticketing tool • for any issues we can raise and clear it • way to ticket track i. request(configuration) ii. incident (severity issue) iii. problem management (code change, too built) iv. change management SVN Tool: (sub version tool): • it is a centralized version control system • open source tool for version control • it used to manage the current and previous version of files like source code, documentation & file. • (SVN tortoise) our version (Apache made)
- 43. 43 43 ANONYMOUS & CURSOR BLOCK: ANONYMOUS BLOCK • PL/SQL block which can be created & used in same session but they will not be stored in server as database object. • It does not have any name assigned to them. Declare Begin Exception(optional) End %type: Used to retrieve datatype of single column form a table %rowtype: Used to retrieve datatype of entire column form a table CURSOR BLOCK • Cursor Stores the result of SQL query and manipulates in temporary work area. • Cursor can hold more than one row but it process row by row (loop). • Cursor holds set of rows called active rows. • We can perform DML operation in cursor by IF statement. • The cursor is a pointer to this context area • Oracle creates context area for processing an SQL statement through the cursor. There are two type of cursor 1. Implicit cursor 2. Explicit cursor 3. Implicit cursor: It is automatically generated by oracle while SQL statement is executed. Explicit cursor: It is defined by user or programmer to gain more control over the context area. SYNTAX: Cursor <cursor name> is Select_statement. Implicit cursor Explicit cursor No need cursor keyword for declare Requires declaration of cursor keyboard returns one row Returns one or more rows Automatically created by Oracle whenever SQL statement is executed Programmer defined cursor for control over context area Simple select query Row by row fetch Default cursor Defined cursor
- 44. 44 44 ATTRIBUTES OF CURSOR: %NOTFOUND, %FOUND, %ISOPEN, %ROWCOUNT. %NOTFOUND: Loop Runs For Multiple Value Output Until Condition Is True Loop runs for all values Returns Boolean result • True→ not fetch record else fetch record %FOUND: Loop Runs For Only One Value Output Until Condition Is False Loop runs for only one value If it is true then fetch records false then not fetch records %ROWCOUNT: To Fetch The No Of Rows Affected Rows In Complete Cursor Record Return numeric value Gives actual count of records that are affected by DML activity %ISOPEN: Returns True If The Cursor Is Open, Else False. Boolean result true/ else falls cursor already opened Difference between Cursor and Ref Cursor Cursor Ref Cursor A cursor is really any SQL statement that runs DML (select, insert, update, delete) on your database. A ref cursor is a pointer to a result set. This is normally used to open a query on the database server, then leave it up to the client to fetch the result it needs. What is the difference between Explicit and Implicit Cursors? An Implicit cursor is one created "automatically" for you by Oracle when you execute a query. It is simpler to code An Explicit cursor is one you create yourself. It takes more code, but gives more control - for example, you can just open-fetch-close if you only want the first record and don't care if there are others DBA_DATA_FILES. COLLECTIONS: • it is an ordered group of elements having the same data type • Each element has a unique subscript that represent its position in the collection • It is one dimension
- 45. 45 45 VARRAY: • It is dense and bounded • Varray variable size array • When you create a varray you must declare a maximum number of columns • They use sequence number as subscript • We can’t delete in VR • We can’t rent only last to first • Stored in a database 10 33 45 51 67 1 2 3 4 5 X(1)=10 , X(4)=51 Index value(above table 1,2,3,4,5) is created by oracle DBMS Collection method: • First/last • Next/prior • Count • Extends • Trim • Delete • Exits Datas.csv(hat file)→server layer path root/script/a,g/ss/file/data→ staying table/delta table Emp_stg)→Target table(query→select→all files) Nested Table: (table of ) • nested table is the column type that hold a set of values • It is prased and unbounded • Main advantage is no limits • It will create new value add boxes • We can delete in nested table • It can be stored in a database Associative array: (table of ( ) index by PLS_integer/ binary_integer): • Set off key values pair • Each key is unique and the key can be either string or integer • Stored in ram level only • It is capable of holding an unspecified number Limit 10: For reduce memory use: Fetch C1 bulk collect into V_RC limit 100;
- 46. 46 46 PLS INTEGER BINARY INTEGER When a PSL-Integer calculation overflow an exception is raised When a binary-Integer calculation overflow no exception is raised It is Subset of binary integer It is Subset of integer Stores data in arithmetic format (requires less storage) Stores data in binary format It is faster than number and binary integer (better performance) It is also faster, but slower than pls_integer It uses machine arithmetic It uses library arithmetic For All For Fetch and insert/ update / delete in one shot Fetch and insert/ update / delete in loop format One for all, only one DML operation We can use multiple DML operation inside for in Loop Bulk binding operation Bulk Binding: Combination of Bulk collect and for all Bulk collect → fetch the data → using ‘select’ For all→ process the data→using ‘insert’,’update’,’delete’. Advantage of bulk collect: • Only one context switch (collect data from PLSQL engine to SQL engine in one loop) • Increases the performance by reducing the interaction between database and PL/SQL engine • Limit clause→ for reduce memory use Disadvantage: • Issues in memory allocation Nested table array V array Nested tables are unbounded. VARRAYs are always bounded (varying arrays have a limited number of entries) Initially dense but can become sparse through deletions. Never sparse. Order is not preserved When you store and retrieve a VARRAY, its element order is preserved Can be indexed Cannot be indexed
- 47. 47 47 Associate array or Index by table Nested table array V array Unbounded i.e. the number of elements it can hold is not pre-defined Unbounded i.e. the number of elements it can hold is not pre-defined Bounded i.e. holds a declared number of elements, though this number can be changed at runtime Can be arbitrary numbers or strings. Need not be sequential. Sequential numbers, starting from one Sequential numbers, starting from one Index by tables can be used in PL/SQL programs only, cannot be stored in the database. Can be stored in the database using equivalent SQL types, and manipulated through SQL. Can be stored in the database using equivalent SQL types, and manipulated through SQL (but with less ease than nested tables) Works as key-value pairs. e.g. Salaries of employees can be stored with unique employee numbers used as subscripts sal(102) := 2000; Similar to one-column database tables. Oracle stores the nested table data in no particular order. But when you retrieve the nested table into a PL/SQL variable, the rows are given consecutive subscripts starting at 1. Standard subscripting syntax e.g. color(3) is the 3rd color in varray color Most flexible. Size can increase/ decrease dynamically. Elements can be added to any position in the list and deleted from any position. Almost like index-by tables, except that subscript values are not as flexible. Deletions are possible from non- contiguous positions. Not very flexible. You must retrieve and update all the elements of the varray at the same time. Hash tables Sets and bags Arrays PROCEDURES: Stored procedure: • It is named P L SQL subprograms • It is compiled and stored in database for repeated execution • It can accept an argument and can return a value • It is a schema object • It improves the performance of an application by reducing network trafficking • It can accept parameter • If procedure is created outside the package then it is called as stored subprogram or standalone subprogram • If procedure is created in package then it is called as packaged subprogram.
- 48. 48 48 Note: • We can create a procedure inside anonymous block • We can create procedure inside package • We can create procedure inside procedure • Used to business logic development • May or may not have return value Local procedure [private procedure]: • Whenever you create a procedure inside the anonymous block it is called local procedure • This procedure doesn’t store in database and cannot be called outside anonymous block Parameters: • This indicates that value must be supplied when you execute the procedure • in , out , in/out To view entire query of a procedure: select * from user_source where name = ’P_first’; Create Or Replace: it would not affect grants which is given to objects and not affect the dependencies select * from user_dependencies create: completely clears the grams and dependencies REF CURSOR: Cursor→static Ref cursor→ dynamic • It is a data type • It will close implicit • entire table result output • mostly give ref cursor to front end user strong ref cursor: • we know structure at compilation time • it returns a value which can be of any data type weak ref cursor: • doesn’t know structure at compilation time • query result will be stored
- 49. 49 49 bind variable: (:Y) • it is a placeholder in SQL statement • by using this you can write a SQL statement that accept inputs or parameter at runtime • it can improve SQL query performance also Hard phrase Soft phrase Query→buffer cache→data block Query→buffer cache Select * from V$SQL order by first_load_time DESC. Each query has unique ID 13 digit EXCEPTIONS: • Exceptions are used to handle error in PLSQL block • The action to be performed when error occurs Rules: • Exception must be declared the declaration section • Exception must be raised in exception section • Exception should be handled exception section SQLERRM→SQL ERROR MESSAGE SQL CODE→ SQL ERROR CODE Type of exceptions: • Pre-defined (oracle error no→error message) • Non-predefined(oracle error no→own message) • User defined(own error no→own message) Pre-defined: • This can be called as system defined exception or unnamed system exception • PLSQL predefined some common Oracle error as exception • 20 predefined exception (SYS_INVALID_ROWID, CURSOR_ALREADY_OPENED, NO_DATA_FOUND, TOO_MANY_ROWS, ZERO_DIVIDE, INVALID_NUMBER, VALUE_ERROR, OTHERS, INVALID_CURSOR) Non-predefined: • The system exception for which oracle doesn’t have name is called non-predefined (or) unnamed system exception. • Hear, we use ‘PRAGMAEXCEPTION_INIT’ is used to bind defined exception to a particular error number of others
- 50. 50 50 Rules for writing exception: • If you use more than one exception in a block then only one exception fires that will be based on first error occurrence. • If you use ‘other’ exception another exception then ‘other’ it must be lost in exception section. User Defined: • Apart from system exception you could explicitly define and raise exception. • In user defined we use ‘RAISE’ keyword to forcibly raise an exception • Error range(-20000 to -20999). Save exception: The save exceptions clause allows the bulk operation to continue past any exceptions, but if any exceptions where raised in the whole operation, then it will jump to the exception handler once the operation is complete. FUNCTIONS: • it is a PLSQL program which can be called as stored function • It must always return a value • It is a compiled and stored in database for repeated execution • It can accept arguments • We can also call to function in select statement • Return only one value for multiple we use out parameter function • Functions compute a value • Function also can be called as part of execution • Function cannot perform DML • Function can use only parameter IN • It is a schema object Note: • We can create function inside the package • We can create function inside anonymous block • We can create function inside the procedure • If a function is created outside the package then it is called stored subprogram • If it is created inside the package then it is called package subprogram What are functions and their usage in SQL? SQL functions are simple code snippets that are frequently used and re-used in database systems for data processing and manipulation. Functions are the measured values. It always performs a specific task. The following rules should be remembered while creating functions:
- 51. 51 51 o A function should have a name, and the name cannot begin with a special character such as @, $, #, or other similar characters. o Functions can only work with the SELECT statements. o Every time a function is called, it compiles. o Functions must return value or result. o Functions are always used with input parameters. SQL categories the functions into two types: o User-Defined Function: Functions created by a user based on their needs are termed user-defined functions. o System Defined Function: Functions whose definition is defined by the system are termed system-defined functions. They are built-in database functions. SQL functions are used for the following purposes: o To perform calculations on data o To modify individual data items o To manipulate the output o To format dates and numbers o To convert data types Procedure Function Procedure perform an action Function performs complete value It can accept and may or may not return a value It can accept the value and must return a value It cannot be called from select statement It can be called from select statement Procedures can have multiple out parameters Function are generally restricted to return a single value Not useful in queries More useful in queries It is slightly easier to call It is not easier to call compared to function PACKAGES: It is group of logically related sub-programs. It is schema object. It has 2 parts 1.)specification and 2.)Body Local or Private Procedure: The subprogram defined in specification should be defined in body. The subprogram defined in body may or may not be defined in specification. Over Loading Concept: When we have some sub program in packages difference in no of parameters, name of parameter, , datatype of parameter. Package Specification: • It contain a declaration • You can decide cursor, type, variable, sub-program, exception and constant • You can create a package specification without package body
- 52. 52 52 • Whatever declared in package specification is global. • Subprogram which is defined in specification should be declared in body. • we can compile only specification Package body: • it contains definitions • it contained definition of subprogram that is listed in package specification • it also contain the definition of subprogram that is listed in the package specification. • It also contains local procedure it will be one time procedure it is also called as private procedure. • You can delete the package body without deleting the package specification. Note: • Subprogram which is defended package may or may not be present in specification. • You can compile specification body by using • We can compile body also. Advantages: • When package subprogram are executed for first time it is loaded to memory, further execution of subprogram doesn’t require disk I/O. • Packages supports Overloading concepts. • Subprogram defend in package specification are global subprogram or global variable in specification. Overloading: [by using assign parameters]: • P1 (difference in number of arguments) • P2 (difference in parameter data type) • P3(difference in their parameter name) Grant execute on (pkg132 systems); SQL query tuning: • Select field instead of select * • Avoid using select distinct • Create join using with inner join [not using word] • Use where instead of having for filter purpose • use wild card operator at the end of phrase only (%) • use limit to sample query result • run your query during off peak hours Pragma serially reusable: • Memory allocation of constant • Declaration in specification
- 53. 53 53 Bodiless packages: • You can use the bodiless packages for execution • Here this variable exists only in this session Performance tuning: • First we will check for the date counts • We will go For the table statistics which place primary role in performance tuning ( no of rows in explain plan is based on status gathered] • If not we use gathered status for all the table • Then we will check for the index and make sure index are in valid state or not • If not we will rebuild the index Block level: • for any block level tuning we will go for DBMS profiler (it’s getting ROWID and long running SQLID then process goes for explain plan • we also get AWR report from DBA Team getting SQL statistics information that is (automated workload repository) from there we get long running SQL ID) • then we take explain plan for the query • From explain plan we get what type of scan it goes for o Table full scan o Index scan o Index unique scan o Index range scan o Index full scan o Index fast full scan • Then we use the hints to change the optimizer plan • We check up on the cardinality, costs and bytes like this performance tuning goes on. PARTITION AND INDEX (ORACLE INDEX):: TABLE PATITIONING:- • Table partition is a method of splitting an object (table or index) into separate partitions based on some criteria. The criteria can be date, number or character. • If table contains more number of rows then queries takes more time to execute a query and table becomes harder to manager. So in that case we use table partitioning to overcome those issues. We can partition Table, Index & Materialized View. • Partition allows table, index and index organized a table to be subdivided into smaller pieces • It is used to reduce the cost and improving performance of application.
- 54. 54 54 Advantages: • Increase performance • Increase availability • Enable storage cost optimization • Enable simple management Where we use: • Tables greater than 2GB • Tables contain historical old data • When content needs to be distributed • when table performance this week What is Partition key? ANS: The partition key is a set of one or more columns that determines the partition for each row. Oracle automatically directs insert, update, and delete operations to the appropriate partition through the use of the partition key. What is use of Partition? ANS: The PARTITION BY clause sets the range of records that will be used for each "GROUP" within the OVER clause. In your example SQL, DEPT_COUNT will return the number of employees within that department for every employee record. What are the types of Partition? ANS: Oracle provides the following partitioning methods: Range Partitioning. List Partitioning. Hash Partitioning. Composite Partitioning Table Partition: • Segmenting the data • Partition allows table, index are sub divided into small pieces • It reduces cost and improves performance of the application When we go for: • In master table • Table greater than 2 GB • Tables contain historically old records • When table performance is weak
- 55. 55 55 Advantages: • Increases performance • Increases availability • Optimize the storage cost • Simpler management Types: • Range partition • List partition • Hash partition • Composite partition Range Partition: CREATE TABLE sales_range (salesman_id NUMBER(5), salesman_name VARCHAR2(30), sales_amount NUMBER(10), sales_date DATE) PARTITION BY RANGE(sales_date) INTERVAL(NUMTOYMINTERVAL(1,'MONTH')) (PARTITION sales_jan2000 VALUES LESS THAN(TO_DATE('02/01/2000','MM/DD/YYYY'))); Interval partition: • Available only after oracle 11g version • When we adding new data, there must be error (not in range) • This overcome by using interval partition • When max limit reaches oracle itself create a partition called interval partition • When we drop the table partition then data also trauncated List partition: (region wise partition): CREATE TABLE sales_list (salesman_id NUMBER(5), salesman_name VARCHAR2(30), sales_state VARCHAR2(20), sales_amount NUMBER(10), sales_date DATE) PARTITION BY LIST(sales_state) (PARTITION sales_west VALUES('CHENNAI', 'MADURAI'), PARTITION sales_east VALUES ('New York', 'VADODRA', 'DELHI'), PARTITION sales_central VALUES('BANG', 'COCHIN'), PARTITION SYS_PART VALUES('COIM'), PARTITION SYS_PAR1 VALUES('TRICHY'), PARTITION sales_other VALUES(DEFAULT));
- 56. 56 56 Automatic: • Only after 12c version • When we insert ‘AAA’,’BBB’ it automatically inserts their loation • Otherwise it create sales_others by own name. Hash Partition: • It is partitioned by datablocks • Most not used • When we don’t know to do partition on which column in that case we go for hash partition Composite Partition: • Combination of any two partition Global index: Create on the table Local index: • Create on each partition • Effective once Prefixed local index: • Create index year_idx On all_fact(sale_date)→ partition key Local (partition sales_jan 2021); Sub-prefixed local index: Create index year_idx on all_fac(sale_amount)→partition key Local(partition sale_jan2021); How to create a partition in already created table? • We go for “exchange partition” • Method: a. New table with all partition b. Load data from old to new c. Rename new table d. Drop a old table TRIGGER: • Trigger is a database object which automatically occurs when a triggering event occurs. • Event fires another event • You can enable & disable trigger
- 57. 57 57 Event option: • DML (insert,delete,update) • DDL (create,alter) • User logon/logoff • System (startup/Shutdown) Used for: • Prevent invalid transaction • Generating values for any derived column • Auditing purpose • To maintain having historic data of core table Restriction: • We cant use DDL in trigger because they have implicit cursor • We cant use commit, savepoint or rollback • We cant call trigger inside any function/procedure • We can call others inside the trigger SELECT * FROM USER_TRIGGER ALTER TRIGGER TRG1 DISABLE Projectin Trigger: We use to capture the history data/table in core schema, it will be capture in the trigger table with userid. Row level trigger Statement level trigger When triggering event takes place many times, that much time trigger is fired When triggering event takes place many times it fires only once to target table For each row clause is present That clause not present Used for data auditing purpose :old word only in row level trigger Used for additional security on the transaction performed in the table Ex: if 1500 rows are to be inserted then 1500 times trigger fires If 1500 rows are to be inserted then only one trigger fires Mutating table / Mutating errors: (ORA-04091) Recursive SQL • If any DML operation is taking place in a table and your trying to make another change in middle of first change. • When we do DML operation on a table, trigger associated with the table automatically fire and make another change (DML) to the same table • This is overcome by using compound trigger • It is 11G new feature
- 58. 58 58 Compound Trigger: More than one trigger in same table in called compound trigger. It fires as: Before statement level follows by Before row level follows by After row level follows by After statement level Pragma autonomous transaction: • Pragma→complier directive • Provide information to the computer • Performs independent transaction • You must use commit or rollback, otherwise we get error ‘ORA-06519’ • Independent transaction between begin & end without affecting entire transaction or other transaction • We can do DDl,,DML in function & procedure using Pragma autonomous transaction. HINTS AND TABLE REGONIZATION: • Optimizer directive • Used to change the optimizer directive plan Hints of Joining Order: • Leading • Ordered • Used to determine in which order to join the table • Optime will go to RBC Select/*+ordered*/from employees; Hints of access path: • Index /* index(emp_dep_x)*/ • No_index /*+no_index(emp_department_lX)*/ • Append • Full Append: • Direct load datablock • Faster • Not stored in buffer/redo logs Hints for parallel execution: /*+parallel(2)*/ → depend upon space
- 59. 59 59 Technique is multithreading: • Use multiple I/O to run fast • We need DBA confirmation & proper server space, then only we use the parallel hint • For this DBA team generate certain formula Hints for Join condition: USE_HASH NO_USE_HASH USE_NL NO_USE_NL USE_MERGE NO_USE_MERGE Example: select/* + no_use_hash*/ from employees; Select * from table (DBMS_xplan.Display()); Types of Scan: 1. Table full scan: • Analyse all records in the table. • For look up table , we go for table full scan 2. Index scan: • When we use primary or unique key column in a where clause • It automatically goes for index unique scan. 3. Index range scan: • When we use range between or limits in a where clause 4. Index fast scan: • When a column used in where clause contains index • All column must contain index 5. Index fast full scan: • When a column used in select clause contain index and also columns used in where clause contain index. 6. Index skip scan: • When we create a composite index (A,B) we call only one composite index column where as skip another column using filters Table recognition: By using this we can remove empty blocks in the table Tablespace→multiple space→multiple extend→datablocks Create table ‘HR’,’Prawin’ (Id number name varchar2(50)) Tablespace A; alter table prawin move to buffer_TB; alter table prawin move to A; (by using this, we can shrink the empty blocks)
- 60. 60 60 NORMALIZATION: What is Normalization? ANS: Normalization is a systematic approach of decomposing tables to eliminate data redundancy and undesirable characteristics like Insertion, Update and Deletion Anomalies. It is a multi-step process that puts data into tabular form by removing duplicated data from the relation tables. What is Normalization in a Database? Normalization is used to minimize redundancy and dependency by organizing fields and table of a database. There are some rules of database normalization which commonly known as Normal From and they are: First normal form(1NF) Second normal form(2NF) Third normal form(3NF) Boyce-Codd normal form(BCNF) Using these steps, the redundancy, anomalies, inconsistency of the data in the database can be removed. What is the primary use of Normalization? Normalization is mainly used to add, delete or modify a field that can be made in a single table. The primary use of Normalization is to remove redundancy and to remove the insert, delete and update distractions. Normalization breaks the table into small partitions and then link them using different relationships so that it will avoid the chances of redundancy. What is Denormalization in a Database? Denormalization is used to access the data from higher or lower normal form of database. It also processes redundancy into a table by incorporating data from the related tables. Denormalization adds required redundant term into the tables so that we can avoid using complex joins and many other complex operations. Denormalization doesn?t mean that normalization will not be done, but the denormalization process takes place after the normalization process. What are the disadvantages of not performing Database Normalization? The major disadvantages are: The occurrence of redundant terms in the database which causes the waste of the space in the disk. Due to redundant terms inconsistency may also occur id any change will be made in the data of one table but not made in the same data of another table then inconsistency will take place, which will lead to the maintenance problem and effects the ACID properties as well.
- 61. 61 61 UNIX: Only lowercase character Double click → copy right click → paste ctrl+c=cut the process pwd→present working directory cd demo →change directory cd .. →previous directory cd user/demo/change→ directly go to the directory mkdir demo→ create directory touch l.txt / touch l.pdf→create a file Is→ print of list of files and sub directory Is-a → hidden files also Is*.txt→find only extension file that given Is-lrt→find list of files with date and time Find l.sql→find specified named file Rm l.txt→delete a Rm -r demo→delete a directory Cp 2.pdf demo→copy a file to another directory Cp-r→copy a directory to another directory Cat 2.sql→open a file in code Edit: Vi l.txt→ edit a file i→insert type the detail wq→ write & quit q→quit/view l.sql→ views in vi tar-cvzf→zip the folder tar-xvzf→unzip the folder grep’demo’l.txt→word Finder [case sensitive] grep-i’demo’l.txt→ word Finder [case insensitive] sed’s/india/tamil/’→replace word/any string sed’s/1/t/g/’→replace letters globally Echo’prawin’→print Prawin=10 Echo $ prawin print 10 Sed ‘5d’ l.txt→ delete the 5th line Sed ‘$d’ l.txt→ delete the last line Sed ‘3,6d’ l.txt→ delete range of line Chmod 777(user/group/others) 4-read(r) 2-write(w) 1-excute(x) 777- give all permissions to all users 651→read write /read execution/ execution
- 62. 62 62 OTHER QUESTIONS: Why we go for Packages? ANS: Packages allow you to encapsulate logically related types, variables, constants, subprograms, cursors, and exceptions in named PL/SQL modules. By doing this, you make each package more reusable, manageable, readable and reliable. What is meant by Autonomous Transaction? ANS: Autonomous transactions allow you to leave the context of the calling transaction, perform an independent transaction, and return to the calling transaction without affecting it's state. The autonomous transaction has no link to the calling transaction, so only committed data can be shared by both transactions What are the types of PRAGMA? ANS: 1. PRAGMA AUTONOMOUS_TRANSACTION 2. PRAGMA EXCEPTION_INIT 3. PRAGMA SERIALLY_REUSABLE 4. PRAGMA RESTRICT_REFERENCES 5. PRAGMA INLINE What is forward declaration? ANS: PL/SQL requires that you declare elements before using them in your code. This declaration makes that program available to be called by other programs even before the program definition. ... Remember that both procedures and functions have a header and a body. What is NOCOPY? ANS: The NOCOPY hint tells the PL/SQL compiler to pass OUT and IN OUT parameters by reference, rather than by value. ... On successful completion of the subprogram the values are copied back to the actual parameters, but unhandled exceptions result in the original parameter values being left unchanged What is the use of Parallel hint? ANS: Let's say a query takes 100 seconds to execute without using parallel hint. If we change DOP to 2 for same query, then ideally the same query with parallel hint will take 50 second. Similarly using DOP as 4 will take 25 seconds. What is Hash Cluster? A row is stored in a hash cluster based on the result of applying a hash function to the row's cluster key value. All rows with the same hash key value are stores together on disk. What is a User_exit? Calls the user exit named in the user_exit_string. Invokes a 3Gl program by name which has been properly linked into your current oracle forms executable.
- 63. 63 63 What is schema? A schema is collection of database objects of a user. What are Roles? Roles are named groups of related privileges that are granted to users or other roles. What is a SNAPSHOT? Snapshots are read-only copies of a master table located on a remote node which is periodically refreshed to reflect changes made to the master table. What are clusters? Clusters are groups of one or more tables physically stores together to share common columns and are often used together. What are ORACLE PRECOMPILERS? A pre compiler is a tool that allows programmers to embed SQL statements in high- level source programs like C, C++, COBOL, etc.The precompiler accepts the source program as input, translates the embedded SQL statements into standard Oracle runtime library calls, and generates a modified source program that one can compile, link, and execute in the usual way. What are the differences between stored procedures and triggers? A stored procedures are compiled collection of programs or SQL statements that live in the database. A stored procedure can access and modify data present in many tables. Also a stored procedure is not associated with any particular database object. But triggers are event-driven special procedures which are attached to a specific database object. What must be installed with ODBC on the client in order for it to work with Oracle? SQLNET and PROTOCOL (for example: TCPIP adapter) layers of the transport programs. What Is Trigger? Triggers are special kind of stored procedures that get executed automatically when an INSERT, UPDATE or DELETE operation takes place on a table. What is the maximum number of triggers, can apply to a single table? 12 triggers What command would you use to create a backup control file? Alter database backup control file to trace. What Is Integrity Constrains? Integrity constraints are used to ensure accuracy and consistency of data in a relational database.
- 64. 64 64 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 stored only once for multiple tables in the cluster. DATA DICTIONARY TABLES:- DICTIONARY :- It is used to find list of data dictionary tables available in oracle. USER_OBJECTS :- It contains list of objects present in the database (i.e., table, index, view, function, type, trigger, package, package body, lob, procedure, function, materialized view, sequence…etc.) USER_TABLES :- It contains list of tables and global temporary tables present in the database. USER_VIEWS :- It contains list of views present in the database. USER_ERRORS :- It contains the error occurred during creating object like procedure, package body, function... etc. USER_TAB_COLUMNS :- It contains list of columns present in the entire table in the database. USER_CONSTRAINTS / USER_CONS_COLUMNS :- It contains the list of constraints which was created by all users in the database. USER_INDEXES :- It contains the list of index created by all users in the database. USER_TRIGGERS :- It contains the list of triggers present in the database. USER_SOURCE :- It contains the entire script on object like procedure, package, package body, function, trigger and type. USER_MVIEWS :- It contains the list of materialized view in the database. USER_SEQUENCES :- It contains the list of sequence present in the database.
- 65. 65 65 ALL_USERS :- It contains list of users who can login into database. What is D.B. link? It is used to fetch data from other database. Database team will create for us. Create public database link MyLink. Connect to user identified by using password Insert into table T1 select star from table T1 @ my link; SCRIPT OF THE TABLE ? DBMS Meta data get ddl ANS: SELECT DBMS_METADATA.get_ddl(object_Type, object_name, owner) FROM ALL_OBJECTS WHERE OWNER = 'OWNER_NAME'; Where can be find the column data type of data table (User_tab_column)? ANS: SELECT DATA_TYPE from INFORMATION_SCHEMA.COLUMNS where table_schema = ’yourDatabaseName’ and table_name = ’yourTableName’. USER_TAB_COLUMNS describes the columns of the tables, views, and clusters owned by the current user. what is global temporary table? ANS: DATA STORED TEMPORARILY. DATA STORED AS LONG AS SESSION OR TRANSACTION LASTS AND IS PRIVATE FOR EACH SESSION. AFTER COMMIT OR DISCONNECTION, THE DATA IS LOST BUT TABLE DEFINITION REMAINS IN D.B. WE CAN STORE THE DATA AT RUNTIME AND AFTER COMPLETING THE OPERATION THE DATA WILL BE DELETED. types of global temporary table? ANS: 1.TRANSACTION SPECIFIC GTT(data will be there until you perform commit/rollback) 2. SESSION SPECIFIC GTT(data will remain till end of the session) difference between on command delete rows and preserve rows ANS: ON COMMIT DELETE ROWS clause indicates the data should be deleted at the end of the transaction, or the end of the session. ON COMMIT PRESERVE ROWS clause indicates that rows should persist beyond the end of the transaction. They will only be removed at the end of the session. can we create view and synonmys and index on temporary table??? We CAN’T create view and synonmys and index on temporary table
- 66. 66 66 I want to store a resume in a table column? By using clob Can we store a image in a table ? By using blob Difference between numbers(5) and number(5,2) Weight Decimal (5,2) means the total number of digits cannot exceed 5 and 2 digits can be placed to the right of the decimal. However, the value 1000.45 in the second line of code above exceeds the specified range of (5, 2) since it means 6 digits in total and throws an overflow error. Can we convert number to CHAR TO_CHAR Can we convert long to lob You can use the ALTER TABLE statement in SQL to convert a LONG column to a LOB column. Can we swap a column A and column B in a table UPDATE T1 SET a = b,b=a; Table: T1 A B 1 2 3 4 5 6 After execution the table will look like: Table: T1 A B 2 1 4 3 6 5 Any All Same like or operator Same like ’and’ operator Any condition All conditions should satisfied. Comparison Operator is must Comparison Operator is must Alias Rename Alias is a temporary name given to a table or column Rename is a permanent name given to a table or column Alias is an alternative name Rename is nothing but a replacement of name
- 67. 67 67 Column : also called this as columns, fields, attributes -1000 columns Rows: also called this as rows records and tuple- no limit Can we create a table to another table? You can create one table from another by adding a SELECT statement at the end of the CREATE TABLE statement: CREATE TABLE new_tbl [AS] SELECT * FROM orig_tbl; Insert into table of subquery (select) Once we can create table based on another table constraints will copy to other table. Can you able to join Nested table into D.B.? Yes, you can join using Table () Why we use create or replace each time? Grant permission of dependency object can not be revoked. What is the difference between pre-select and pre-query? A pre-query trigger fire before the query executes and fire once while you try to query. With the help of this trigger you can modify the where clause part dynamically. Pre-select query fires during the execute query and count query processing after Oracle forms construct the select statement to be issued, but before the statement is actually issued. Pre-query trigger fires before Pre-select trigger. Explain character-manipulation functions? Explains its different types in SQL. Character-manipulation functions are used to change, extract, and alter the character string. When one or more characters and words are passed into the function, the function will perform its operation on those input strings and return the result. The following are the character manipulation functions in SQL: A) CONCAT: This function is used to join two or more values together. It always appends the second string into the end of the first string. For example: Input: SELECT CONCAT ('Information-', 'technology') FROM DUAL; Output: Information-technology B) SUBSTR: It is used to return the portion of the string from a specified start point to an endpoint. For example: Input: SELECT SUBSTR ('Database Management System', 9, 11) FROM DUAL; Output: Management C) LENGTH: This function returns the string's length in numerical value, including the blank spaces. For example: Input: SELECT LENGTH ('Hello Javatpoint') FROM DUAL; Output: 16 D) INSTR: This function finds the exact numeric position of a specified character or word in a given string. For example: Input: SELECT INSTR ('Hello Javatpoint', 'Javatpoint'); Output: 7
- 68. 68 68 E) LPAD: It returns the padding of the left-side character value for right-justified value. For example: Input: SELECT LPAD ('200', 6,'*'); Output: ***200 F) RPAD: It returns the padding of the right-side character value for left-justified value. For example: Input: SELECT RPAD ('200', 6,'*'); Output: 200*** G) TRIM: This function is used to remove all the defined characters from the beginning, end, or both. It also trimmed extra spaces. For example: Input: SELECT TRIM ('A' FROM 'ABCDCBA'); Output: BCDCB H) REPLACE: This function is used to replace all occurrences of a word or portion of the string (substring) with the other specified string value. For example: Input: SELECT REPLACE ( 'It is the best coffee at the famous coffee shop.', 'coffee', 'tea'); Output: It is the best tea at the famous tea shop. What are tables and fields in the database? A table is a set of organized data in the form of rows and columns. It enables users to store and display records in the structure format. Fields are the components to provide the structure for the table. It stores the same category of data in the same data type. What is an inconsistent dependency? An Inconsistent dependency refers to the difficulty of getting relevant data due to a missing or broken path to the data. It leads users to search the data in the wrong table, resulting in an error as an output. Is it possible to sort a column using a column alias? Yes. We can use the alias method in the ORDER BY instead of the WHERE clause for sorting a column. What is the SQL query to display the current date? There is a built-in function in SQL called GetDate(), which is used to return the current timestamp. What is the ACID property in a database? The ACID properties are meant for the transaction that goes through a different group of tasks. A transaction is a single logical order of data. It provides properties to maintain consistency before and after the transaction in a database. It also ensures that the data transactions are processed reliably in a database system. The ACID property is an acronym for Atomicity, Consistency, Isolation, and Durability.
- 69. 69 69 BETWEEN Operator IN Operator This operator is used to selects the range of data between two values. The values can be numbers, text, and dates as well. It is a logical operator to determine whether or not a specific value exists within a set of values. This operator reduces the use of multiple OR conditions with the query. It returns records whose column value lies in between the defined range. It compares the specified column's value and returns the records when the match exists in the set of values. The following syntax illustrates this operator: SELECT * FROM table_name WHERE column_name BETWEEN 'value1' AND 'value2'; The following syntax illustrates this operator: SELECT * FROM table_name WHERE column_name IN ('value1','value 2'); How to write an SQL query to find students' names start with 'A'? SELECT * FROM student WHERE stud_name like 'A%'; Write the SQL query to get the third maximum salary of an employee from a table named employees? SELECT salary FROM (SELECT salary FROM employees ORDER BY salary DESC LIMIT 3) AS Temp ORDER BY salary LIMIT 1; Which function is used to return remainder in a division operator in SQL? The MOD function returns the remainder in a division operation. What are SQL comments? Comments are explanations or annotations in SQL queries that are readable by programmers. It's used to make SQL statements easier to understand for humans. During the parsing of SQL code, it will be ignored. Comments can be written on a single line or across several lines. o Single Line Comments: It starts with two consecutive hyphens (--). o Multi-line Comments: It starts with /* and ends with */. What is PL/SQL? PL/SQL stands for procedural language extension to SQL. It supports procedural features of programming language and SQL both. It was developed by Oracle Corporation in early of 90's to enhance the capabilities of SQL.
- 70. 70 70 What is the purpose of using PL/SQL? PL/SQL is an extension of SQL. While SQL is non-procedural, PL/SQL is a procedural language designed by Oracle. It is invented to overcome the limitations of SQL. What are the most important characteristics of PL/SQL? A list of some notable characteristics: 6.9M 151 HTML Tutorial o PL/SQL is a block-structured language. o It is portable to all environments that support Oracle. o PL/SQL is integrated with the Oracle data dictionary. o Stored procedures help better sharing of application. What is PL/SQL table? Why it is used? Objects of type tables are called PL/SQL tables that are modeled as database table. We can also say that PL/SQL tables are a way to providing arrays. Arrays are like temporary tables in memory that are processed very quickly. PL/SQL tables are used to move bulk data. They simplifies moving collections of data. What are the datatypes available in PL/SQL? There are two types of datatypes in PL/SQL: 1. Scalar datatypes Example are NUMBER, VARCHAR2, DATE, CHAR, LONG, BOOLEAN etc. 2. Composite datatypes Example are RECORD, TABLE etc. What is the basic structure of PL/SQL? PL/SQL uses BLOCK structure as its basic structure. Each PL/SQL program consists of SQL and PL/SQL statement which form a PL/SQL block. PL/SQL block contains 3 sections. 1. The Declaration Section (optional) 2. The Execution Section (mandatory) 3. The Exception handling Section (optional) What is exception? What are the types of exceptions? Exception is an error handling part of PL/SQL. There are two type of exceptions: pre_defined exception and user_defined exception. How to write a single statement that concatenates the words ?Hello? and ?World? and assign it in a variable named Greeting? Greeting := 'Hello' || 'World'; Does PL/SQL support CREATE command? No. PL/SQL doesn't support the data definition commands like CREATE.
- 71. 71 71 What is the difference between FUNCTION, PROCEDURE AND PACKAGE in PL/SQL? Function: The main purpose of a PL/SQL function is generally to compute and return a single value. A function has a return type in its specification and must return a value specified in that type. Procedure: A procedure does not have a return type and should not return any value but it can have a return statement that simply stops its execution and returns to the caller. A procedure is used to return multiple values otherwise it is generally similar to a function. Package: A package is schema object which groups logically related PL/SQL types , items and subprograms. You can also say that it is a group of functions, procedure, variables and record type statement. It provides modularity, due to this facility it aids application development. It is used to hide information from unauthorized users. Write a unique difference between a function and a stored procedure. A function returns a value while a stored procedure doesn?t return a value. How exception is different from error? Whenever an Error occurs Exception arises. Error is a bug whereas exception is a warning or error condition. What is the main reason behind using an index? Faster access of data blocks in the table. What are PL/SQL exceptions? Tell me any three. 1. Too_many_rows 2. No_Data_Found 3. Value_error 4. Zero_error etc. How do you declare a user-defined exception? You can declare the User defined exceptions under the DECLARE section, with the keyword EXCEPTION. Syntax: 1. <exception_name> EXCEPTION; How many types of triggers exist in PL/SQL? There are 12 types of triggers in PL/SQL that contains the combination of BEFORE, AFTER, ROW, TABLE, INSERT, UPDATE, DELETE and ALL keywords. o BEFORE ALL ROW INSERT o AFTER ALL ROW INSERT o BEFORE INSERT o AFTER INSERT etc.
- 72. 72 72 What is the maximum number of triggers, you can apply on a single table? 12 triggers. What are some predefined exceptions in PL/SQL? A list of predefined exceptions in PL/SQL: o DUP_VAL_ON_INDEX o ZERO_DIVIDE o NO_DATA_FOUND o TOO_MANY_ROWS o CURSOR_ALREADY_OPEN o INVALID_NUMBER o INVALID_CURSOR o PROGRAM_ERROR o TIMEOUT _ON_RESOURCE o STORAGE_ERROR o LOGON_DENIED o VALUE_ERROR o etc. What is a trigger in PL/SQL? A trigger is a PL/SQL program which is stored in the database. It is executed immediately before or after the execution of INSERT, UPDATE, and DELETE commands. What is the difference between execution of triggers and stored procedures? A trigger is automatically executed without any action required by the user, while, a stored procedure is explicitly invoked by the user. What happens when a trigger is associated to a view? When a trigger is associated to a view, the base table triggers are normally enabled. What is the usage of WHEN clause in trigger? A WHEN clause specifies the condition that must be true for the trigger to be triggered. How to disable a trigger name update_salary? ALTER TRIGGER update_salary DISABLE; Which command is used to delete a trigger? DROP TRIGGER command. what are the two virtual tables available at the time of database trigger execution? Table columns are referred as THEN.column_name and NOW.column_name. For INSERT related triggers, NOW.column_name values are available only. For DELETE related triggers, THEN.column_name values are available only. For UPDATE related triggers, both Table columns are available.
- 73. 73 73 What is stored Procedure? A stored procedure is a sequence of statement or a named PL/SQL block which performs one or more specific functions. It is similar to a procedure in other programming languages. It is stored in the database and can be repeatedly executed. It is stored as schema object. It can be nested, invoked and parameterized. What are the different schemas objects that can be created using PL/SQL? o Stored procedures and functions o Packages o Triggers o Cursors What do you know by PL/SQL Cursors? Oracle uses workspaces to execute the SQL commands. When Oracle processes a SQL command, it opens an area in the memory called Private SQL Area. This area is identified by the cursor. It allows programmers to name this area and access it?s information. What is the difference between the implicit and explicit cursors? Implicit cursor is implicitly declared by Oracle. This is a cursor to all the DDL and DML commands that return only one row. Explicit cursor is created for queries returning multiple rows. What will you get by the cursor attribute SQL%ROWCOUNT? The cursor attribute SQL%ROWCOUNT will return the number of rows that are processed by a SQL statement. What will you get by the cursor attribute SQL%FOUND? It returns the Boolean value TRUE if at least one row was processed. What will you get by the cursor attribute SQL%NOTFOUND? It returns the Boolean value TRUE if no rows were processed. What do you understand by PL/SQL packages? A PL/SQL package can be specified as a file that groups functions, cursors, stored procedures, and variables in one place. What are the two different parts of the PL/SQL packages? PL/SQL packages have the following two parts: Specification part: It specifies the part where the interface to the application is defined. Body part: This part specifies where the implementation of the specification is defined. Which command is used to delete a package? The DROP PACKAGE command is used to delete a package.
- 74. 74 74 How to execute a stored procedure? There are two way to execute a stored procedure. From the SQL prompt, write EXECUTE or EXEC followed by procedure_name. 1. EXECUTE or [EXEC] procedure_name; Simply use the procedure name 1. procedure_name; What are the advantages of stored procedure? Modularity, extensibility, reusability, Maintainability and one time compilation. What is the difference between syntax error and runtime error? A syntax error can be easily detected by a PL/SQL compiler. For example: incorrect spelling etc. while, a runtime error is handled with the help of exception-handling section in a PL/SQL block. For example: SELECT INTO statement, which does not return any rows. Explain the Commit statement? Following conditions are true for the Commit statement: o Other users can see the data changes made by the transaction. o The locks acquired by the transaction are released. o The work done by the transaction becomes permanent. What is mutating table error? Mutating table error is occurred when a trigger tries to update a row that it is currently using. It is fixed by using views or temporary tables. What is consistency? Consistency simply means that each user sees the consistent view of the data. Consider an example: there are two users A and B. A transfers money to B's account. Here the changes are updated in A's account (debit) but until it will be updated to B's account (credit), till then other users can't see the debit of A's account. After the debit of A and credit of B, one can see the updates. That?s consistency. What is cursor and why it is required? A cursor is a temporary work area created in a system memory when an SQL statement is executed. A cursor contains information on a select statement and the row of data accessed by it. This temporary work area stores the data retrieved from the database and manipulate this data. A cursor can hold more than one row, but can process only one row at a time. Cursor are required to process rows individually for queries.