Practical PostgreSQL

Begin

Starts a chained-mode transaction block.

Synopsis

BEGIN [ WORK | TRANSACTION ]

Parameters

WORK | TRANSACTION

A pair of optional noise keywords. They can be ignored, or used to make your SQL more readable.

Results

BEGIN

The message returned when a transaction begins.

NOTICE: BEGIN: already a transaction in progress

The notice returned if a transaction is already in progress within your PostgreSQL session. You cannot nest multiple transactions. The transaction you have in progress is not altered when this happens.

Description

PostgreSQL executes transactions in unchained mode by default. Also called autocommit, this mode encapsulates each user statement in an implicit transaction, and automatically finalizes the transaction by either committing the modification, or performing a rollback, depending on whether or not the execution was successful.

Using BEGIN specifies that you want to enter a transaction block using chained mode, in which statements will be queued by the database, and then sent in a single transaction when the database receives a COMMIT command. Alternatively, the queued statements can be discarded by a ROLLBACK, or by an unexpected disconnection.

Chained mode can be useful when you are working with multiple related tables, and also to increase database performance in general. Executing statements in chained mode uses less CPU and disk resources, as there is only one commit needed per block of statements executed.

When a transaction is committed, the database will attempt to ...