BEGIN

Name

BEGIN -- start a transaction block

Synopsis

BEGIN [ WORK | TRANSACTION ]

Description

By default, 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). BEGIN initiates a transaction block, that is, all statements after BEGIN command will be executed in a single transaction until an explicit COMMIT or ROLLBACK. 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 changing several related tables: 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.

Diagnostics

BEGIN

This signifies that a new transaction has been started.

WARNING: BEGIN: already a transaction in progress

This indicates that a transaction was already in progress. The current transaction is not affected.

Notes

START TRANSACTION has the same functionality as BEGIN.

Use COMMIT or ROLLBACK to terminate a transaction.

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.