BEGIN
BEGIN — start a transaction block
Synopsis
BEGIN [ WORK | TRANSACTION ] [transaction_mode[, ...] ]wheretransaction_modeis one of: ISOLATION LEVEL { SERIALIZABLE | REPEATABLE READ | READ COMMITTED | READ UNCOMMITTED } READ WRITE | READ ONLY [ NOT ] DEFERRABLE
Description
BEGIN initiates a transaction block, that is, all statements after aBEGIN command will be executed in a single transaction until an explicitCOMMIT orROLLBACK is given. By default (withoutBEGIN),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.
If the isolation level, read/write mode, or deferrable mode is specified, the new transaction has those characteristics, as ifSET TRANSACTION was executed.
Parameters
WORKTRANSACTIONOptional key words. They have no effect.
Refer toSET TRANSACTION for information on the meaning of the other parameters to this statement.
Notes
START TRANSACTION has the same functionality asBEGIN.
UseCOMMIT orROLLBACK to terminate a transaction block.
IssuingBEGIN when already inside a transaction block will provoke a warning message. The state of the transaction is not affected. To nest transactions within a transaction block, use savepoints (seeSAVEPOINT).
For reasons of backwards compatibility, the commas between successivetransaction_modes can be omitted.
Examples
To begin a transaction block:
BEGIN;
Compatibility
BEGIN is aPostgreSQL language extension. It is equivalent to the SQL-standard commandSTART TRANSACTION, whose reference page contains additional compatibility information.
TheDEFERRABLEtransaction_mode is aPostgreSQL language extension.
Incidentally, theBEGIN 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.