Saturday, 19 November 2011


Transaction Control Language (TCL)


Transaction control statements manage changes made by DML statements.
What is a Transaction?
A transaction is a set of SQL statements which Oracle treats as a Single Unit. i.e. all the statements should execute successfully or none of the statements should execute.
To control transactions Oracle does not made permanent any DML statements unless you commit it. If you don’t commit the transaction and power goes off or system crashes then the transaction is roll backed.
TCL Statements available in Oracle are
COMMIT       :Make changes done in  transaction permanent.
ROLLBACK  :Rollbacks the state of database to the last commit point.
SAVEPOINT :Use to specify a point in transaction to which later you can rollback.

COMMIT

To make the changes done in a transaction permanent issue the COMMIT statement.
The syntax of COMMIT Statement is
COMMIT  [WORK]  [COMMENT ‘your comment’];
WORK is optional.
COMMENT is also optional, specify this if you want to identify this transaction in data dictionary DBA_2PC_PENDING.
Example
insert into emp (empno,ename,sal) values (101,’Abid’,2300);
commit;


ROLLBACK


To rollback the changes done in a transaction give rollback statement. Rollback restore the state of the database to the last commit point.


Example :
delete from emp;
rollback;          /* undo the changes */


SAVEPOINT


Specify a point in a transaction to which later you can roll back.

Example

insert into emp (empno,ename,sal) values (109,’Sami’,3000);
savepoint a;
insert into dept values (10,’Sales’,’Hyd’);
savepoint b;
insert into salgrade values (‘III’,9000,12000);

Now if you give

rollback to a;

Then  row from salgrade table and dept will be roll backed. Now you can commit the row inserted into emp table or rollback the transaction.

If you give

rollback to b;

Then row inserted into salgrade table will be roll backed. Now you can commit the row inserted into dept table and emp table or rollback to savepoint a or completely roll backed the transaction.

If you give

rollback;
 SQL GUIDE
Then the whole transactions is roll backed.

If you give

commit;

Then the whole transaction is committed and all savepoints are removed.

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