NAME
BEGIN − start a transaction block
SYNOPSIS
BEGIN [ WORK | TRANSACTION ]
DESCRIPTION
BEGIN initiates a transaction block, that is, all statements after BEGIN command will be executed in a single transaction until an explicit COMMIT [commit(7)] or ROLLBACK [rollback(l)] is given. By default (without BEGIN), PostgreSQL executes transactions in ’’autocommit’’ mode, that is, each statement is executed in its own transaction and a commit is implicitly performed at the end of the statement (if execution was successful, otherwise a rollback is done).
Statements are executed more quickly in a transaction block, because transaction start/commit requires significant CPU and disk activity. Execution of multiple statements inside a transaction is also useful to ensure consistency when making several related changes: other sessions will be unable to see the intermediate states wherein not all the related updates have been done.
PARAMETERS
|
WORK |
TRANSACTION
Optional key words. They have no effect.
NOTES
START TRANSACTION [start_transaction(7)] has the same functionality as BEGIN.
Use COMMIT [commit(7)] or ROLLBACK [rollback(7)] to terminate a transaction block.
Issuing BEGIN when already inside a transaction block will provoke a warning message. The state of the transaction is not affected.
EXAMPLES
To begin a transaction block:
BEGIN;
COMPATIBILITY
BEGIN is a PostgreSQL language extension. There is no explicit BEGIN command in the SQL standard; transaction initiation is always implicit and it terminates either with a COMMIT or ROLLBACK statement.
Other relational database systems may offer an autocommit feature as a convenience.
Incidentally, the BEGIN key word is used for a different purpose in embedded SQL. You are advised to be careful about the transaction semantics when porting database applications.
SEE ALSO
COMMIT [commit(7)], ROLLBACK [rollback(l)]