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What is Transaction...? And what are Comment, Roll back n
Save point..?
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Answer Posted / saifudheen
n database technologies, a rollback is an operation which returns the database to some previous state. Rollbacks are important for database integrity, because they mean that the database can be restored to a clean copy even after erroneous operations are performed. They are crucial for recovering from database server crashes; by rolling back any transaction which was active at the time of the crash, the database is restored to a consistent state.
In SQL, ROLLBACK is a command that causes all data changes since the last BEGIN WORK, or START TRANSACTION to be discarded by the relational database management system (RDBMS), so that the state of the data is "rolled back" to the way it was before those changes were made.
A ROLLBACK statement will also release any existing savepoints that may be in use.
A SAVEPOINT is a way of implementing subtransactions (also known as nested transactions) within a relational database management system by indicating a point within a transaction that can be "rolled back to" without affecting any work done in the transaction before the savepoint was created. Multiple savepoints can exist within a single transaction. Savepoints are useful for implementing complex error recovery in database applications — if an error occurs in the midst of a multiple-statement transaction, the application may be able to recover from the error (by rolling back to a savepoint) without needing to abort the entire transaction.
A savepoint can be declared by issuing a SAVEPOINT name statement. All changes made after a savepoint has been declared can be undone by issuing a ROLLBACK TO SAVEPOINT name command. Issuing RELEASE SAVEPOINT name will cause the named savepoint to be discarded, but will not otherwise affect anything. Issuing the commands ROLLBACK or COMMIT will also discard any savepoints created since the start of the main transaction.
Savepoints are supported in some form or other in database systems like PostgreSQL, Oracle, Microsoft SQL Server, MySQL, DB2, SQLite (since 3.6.8), Firebird and Informix (since version 11.50xC3). Savepoints are also defined in the SQL standard.
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