e computer notes - Manipulating data

Manipulating Data
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Objectives
After completing this lesson, you should be able to
do the following:
" Describe each DML statement
" Insert rows into a table
" Update rows in a table
" Delete rows from a table
" Merge rows in a table
" Control transactions

Data Manipulation Language
"A DML statement is executed when you:
Add new rows to a table
Modify existing rows in a table
Remove existing rows from a table
"A transaction consists of a collection of DML
statements that form a logical unit of work.

Adding a New Row to a Table
New
EPARTMENTS row
«insert a new row
into the
DEPARMENTS
table «

The INSERT Statement Syntax
" Add new rows to a table by using the INSERT
statement.
INSERT INTO table [(column [, column...])]
VALUES (value [, value...]);
8
-
5
Only one row is inserted at a time with this syntax.

Inserting New Rows
"Insert a new row containing values for each
column.
"List values in the default order of the columns in
the table.
" Optionally, list the columns in the INSERT clause.
INSERT INTO departments(department_id, department_name,
manager_id, location_id)
VALUES (70, 'Public Relations', 100, 1700);
1 row created.
" Enclose character and date values within single
quotation marks.

Inserting Rows with Null Values
" Implicit method: Omit the column from the
column list.
INSERT INTO departments (department_id,
department_name )
VALUES (30, 'Purchasing');
1 row created.
" Explicit method: Specify the NULL keyword in the
VALUES clause.
INSERT INTO departments
VALUES (100, 'Finance', NULL, NULL);
1 row created.

Inserting Special Values
The SYSDATE function records the current date
and time.
INSERT INTO employees (employee_id,
first_name, last_name,
email, phone_number,
hire_date, job_id, salary,
commission_pct, manager_id,
department_id)
VALUES (113,
'Louis', 'Popp',
'LPOPP', '515.124.4567',
SYSDATE, 'AC_ACCOUNT', 6900,
NULL, 205, 100);
1 row created.

Inserting Specific Date Values
"Add a new employee.
INSERT INTO employees
VALUES (114,
'Den', 'Raphealy',
'DRAPHEAL', '515.127.4561',
TO_DATE('FEB 3, 1999', 'MON DD, YYYY'),
'AC_ACCOUNT', 11000, NULL, 100, 30);
1 row created.
" Verify your addition.

Creating a Script
"Use & substitution in a SQL statement to prompt
for values.
"& is a placeholder for the variable value.
(department_id, department_name, location_id)
VALUES(&department_id, '&department_name',&location);
1 row created.

Copying Rows
from Another Table
" Write your INSERT statement with a subquery.
INSERT INTO sales_reps(id, name, salary, commission_pct)
SELECT employee_id, last_name, salary, commission_pct
FROM employees
WHERE job_id LIKE '%REP%';
4 rows created.
" Do not use the VALUES clause.
"Match the number of columns in the INSERT
clause to those in the subquery.

Changing Data in a Table
EMPLOYEES
Update rows in the EMPLOYEES table.

The UPDATE Statement Syntax
" Modify existing rows with the UPDATE statement.
UPDATE table
SET column == value [, column == value, ...]
[WHERE condition];
8 -
1
Update more than one row at a time, if required.
3

e computer notes - Manipulating data

Updating Rows in a Table
"Specific row or rows are modified if you specify
the WHERE clause.
UPDATE employees
SET department_id = 70
WHERE employee_id = 113;
1 row updated.
"All rows in the table are modified if you omit the
WHERE clause.
UPDATE copy_emp SET
department_id = 110;
22 rows updated.

Updating Two Columns with a Subquery
Update employee 114¶s job and salary to match that of
employee 205.
UPDATE employees
SET job_id = (SELECT job_id FROM
employees
WHERE employee_id = 205),
salary = (SELECT salary
FROM employees
WHERE employee_id = 205)
1 row updated.

Updating Rows Based
on Another Table
Use subqueries in UPDATE statements to update rows
in a table based on values from another table.
UPDATE copy_emp
SET department_id = (SELECT department_id
FROM employees
WHERE employee_id = 100)
WHERE job_id = (SELECT job_id
FROM employees
WHERE employee_id = 200);
1 row updated.

Updating Rows:
Integrity Constraint Error
UPDATE employees
SET department_id = 55
WHERE department_id = 110;
UPDATE employees
*
ERROR at line 1:
ORA-02291: integrity constraint (HR.EMP_DEPT_FK)
violated - parent key not found
Department number 55 does not exist

Removing a Row from a Table
DEPARTMENTS
Delete a row from the DEPARTMENTS table.

The DELETE Statement
You can remove existing rows from a table by using
the DELETE statement.
DELETE [FROM] table
[WHERE condition];

Deleting Rows from a Table
" Specific rows are deleted if you specify the WHERE
clause.
DELETE FROM departments
WHERE department_name = 'Finance';
1 row deleted.
All rows in the table are deleted if you omit the"
WHERE clause.
DELETE FROM copy_emp;
22 rows deleted.

Deleting Rows Based
on Another Table
Use subqueries in DELETE statements to remove rows
from a table based on values from another table.
DELETE FROM employees
WHERE department_id =
(SELECT department_id
FROM departments
WHERE department_name LIKE '%Public%');
1 row deleted.

Deleting Rows:
Integrity Constraint Error
*
Error at Line 1:
ORA-02292: integrity constraint (HR.EMP_DEPT_FK)
violated - child record found

Using a Subquery in an INSERT Statement
INSERT INTO
(SELECT employee_id, last_name email,
hire_date, job_id, salary,
department_id
FROM employees
WHERE department_id = 50) VALUES (99999,
'Taylor', 'DTAYLOR', TO_DATE('07-JUN-99', 'DD-
MON-RR'), 'ST_CLERK', 5000, 50);
1 row created.

Using a Subquery in an INSERT Statement
SELECT employee_id, last_name, email, hire_date,
job_id, salary, department_id
FROM employees

Using the WITH CHECK OPTION Keyword on
DML Statements
"A subquery is used to identify the table and
columns of the DML statement.
"The WITH CHECK OPTION keyword prohibits you
from changing rows that are not in the subquery.
INSERT INTO (SELECT employee_id, last_name, email,
hire_date, job_id, salary
FROM employees
WHERE department_id = 50 WITH CHECK OPTION)
VALUES (99998, 'Smith', 'JSMITH',
TO_DATE('07-JUN-99', 'DD-MON-RR'),
'ST_CLERK', 5000);
INSERT INTO
*
ERROR at line 1:
ORA-01402: view WITH CHECK OPTION where-clause violation

Overview of the Explicit Default Feature
"With the explicit default feature, you can use the
DEFAULT keyword as a column value where the
column default is desired.
"The addition of this feature is for compliance with
the SQL: 1999 Standard.
"This allows the user to control where and when
the default value should be applied to data.
"Explicit defaults can be used in INSERT and
UPDATE statements.

Using Explicit Default Values
" DEFAULT with INSERT:
(department_id, department_name, manager_id)
VALUES (300, 'Engineering', DEFAULT);
" DEFAULT with UPDATE:
UPDATE departments
SET manager_id = DEFAULT WHERE department_id = 10;

The MERGE Statement
"Provides the ability to conditionally update or
insert data into a database table
"Performs an UPDATE if the row exists, and an
INSERT if it is a new row:
Avoids separate updates
Increases performance and ease of use
Is useful in data warehousing applications

The MERGE Statement Syntax
You can conditionally insert or update rows in a
table by using the MERGE statement.
MERGE INTO table_name table_alias
USING (table|view|sub_query) alias
ON (join condition)
WHEN MATCHED THEN
UPDATE SET
col1 = col_val1,
col2 = col2_val
WHEN NOT MATCHED THEN
INSERT (column_list)
VALUES
(column_values);

Merging Rows
Insert or update rows in the COPY_EMP table to match the
EMPLOYEES table.
MERGE INTO copy_emp c
USING employees e
ON (c.employee_id = e.employee_id)
WHEN MATCHED THEN
UPDATE SET
c.first_name = e.first_name,
c.last_name = e.last_name,
c.department_id = e.department_id
INSERT VALUES(e.employee_id, e.first_name, e.last_name,
e.email, e.phone_number, e.hire_date, e.job_id,
e.salary, e.commission_pct, e.manager_id,
e.department_id);

Merging Rows
SELECT *
FROM COPY_EMP;
no rows selected
MERGE INTO copy_emp c
USING employees
ON (c.employee_id = e.employee_id)
WHEN MATCHED THEN
UPDATE SET
INSERT VALUES...;
SELECT *
FROM COPY_EMP; 20
rows selected.

Database Transactions
A database transaction consists of one of the
following:
" DML statements which constitute one consistent
change to the data
" One DDL statement
" One DCL statement

Database Transactions
"Begin when the first DML SQL statement is
executed
"End with one of the following events:
A COMMIT or ROLLBACK statement is issued A
DDL or DCL statement executes (automatic
commit)
The user exits iSQL*Plus
The system crashes

Advantages of COMMIT
and ROLLBACK Statements
With COMMIT and ROLLBACK statements, you can:
" Ensure data consistency
" Preview data changes before making changes
permanent
" Group logically related operations

Controlling Transactions
Time COMMIT
Transaction
DELETE
SAVEPOINT A
INSERT
UPDATE
SAVEPOINT B
INSERT ROLLBACK ROLLBACK ROLLBA
to SAVEPOINT B to SAVEPOINT A

Rolling Back Changes
to a Marker
"Create a marker in a current transaction by using
the SAVEPOINT statement.
" Roll back to that marker by using the ROLLBACK TO
SAVEPOINT statement.
UPDATE...
SAVEPOINT update_done;
Savepoint created.
INSERT...
ROLLBACK TO update_done;
Rollback complete.

Implicit Transaction Processing
"An automatic commit occurs under the following
circumstances:
DDL statement is issued
DCL statement is issued
Normal exit from iSQL*Plus, without explicitly issuing
COMMIT or ROLLBACK statements "An automatic
rollback occurs under an abnormal
termination of iSQL*Plus or a system failure.

State of the Data
Before COMMIT or ROLLBACK
" The previous state of the data can be recovered.
" The current user can review the results of the DML
operations by using the SELECT statement.
"Other users cannot view the results of the DML
statements by the current user.
"The affected rows are locked; other users cannot change
the data within the affected rows.

State of the Data after COMMIT
" Data changes are made permanent in the database.
" The previous state of the data is permanently lost.
" All users can view the results.
" Locks on the affected rows are released; those rows
are available for other users to manipulate.
" All savepoints are erased.

Committing Data
" Make the changes.
DELETE FROM employees
1 row deleted.
VALUES (290, 'Corporate Tax', NULL, 1700); 1
row inserted.
"
Commit the changes.
COMMIT;
Commit complete.

State of the Data After ROLLBACK
Discard all pending changes by using the ROLLBACK
statement:
" Data changes are undone.
" Previous state of the data is restored.
" Locks on the affected rows are released.
DELETE FROM copy_emp;
22 rows deleted.
ROLLBACK;
Rollback complete.

Statement-Level Rollback
" If a single DML statement fails during execution,
only that statement is rolled back.
" The Oracle server implements an implicit
savepoint.
" All other changes are retained.
" The user should terminate transactions explicitly
by executing a COMMIT or ROLLBACK statement.

Read Consistency
"Read consistency guarantees a consistent view of
the data at all times.
"Changes made by one user do not conflict with
changes made by another user.
"Read consistency ensures that on the same data:
Readers do not wait for writers.
Writers do not wait for readers.

Implementation of Read Consistency
User A
UPDATE employees Data
SET salary = 7000 blocks
WHERE last_name = 'Goyal';
Rollback
segments
changed
andSELECT *
FROM userA.employees; Read unchanged
dataconsistent
beforeimage
change
³old´ data
ser B

Locking
In an Oracle database, locks:
" Prevent destructive interaction between
concurrent transactions
" Require no user action
" Automatically use the lowest level of
restrictiveness
" Are held for the duration of the transaction
" Are of two types: explicit locking and implicit
locking

Implicit Locking
" Two lock modes:
Exclusive: Locks out other users
Share: Allows other users to access
" High level of data concurrency:
DML: Table share, row exclusive
Queries: No locks required
DDL: Protects object definitions
" Locks held until commit or rollback

e computer notes - Manipulating data

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