BEGIN(7)

NAME

   BEGIN - start a transaction block

SYNOPSIS

   BEGIN [ WORK | TRANSACTION ] [ transaction_mode [, ...] ]

   where transaction_mode is 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 a
   BEGIN command will be executed in a single transaction until an
   explicit COMMIT(7) or ROLLBACK(7) 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.

   If the isolation level, read/write mode, or deferrable mode is
   specified, the new transaction has those characteristics, as if SET
   TRANSACTION (SET_TRANSACTION(7)) was executed.

PARAMETERS

   WORK
   TRANSACTION
       Optional key words. They have no effect.

   Refer to SET TRANSACTION (SET_TRANSACTION(7)) for information on the
   meaning of the other parameters to this statement.

NOTES

   START TRANSACTION (START_TRANSACTION(7)) has the same functionality as
   BEGIN.

   Use COMMIT(7) or 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. To nest
   transactions within a transaction block, use savepoints (see
   SAVEPOINT(7)).

   For reasons of backwards compatibility, the commas between successive
   transaction_modes can be omitted.

EXAMPLES

   To begin a transaction block:

       BEGIN;

COMPATIBILITY

   BEGIN is a PostgreSQL language extension. It is equivalent to the
   SQL-standard command START TRANSACTION (START_TRANSACTION(7)), whose
   reference page contains additional compatibility information.

   The DEFERRABLE transaction_mode is a PostgreSQL language extension.

   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(7), ROLLBACK(7), START TRANSACTION (START_TRANSACTION(7)),
   SAVEPOINT(7)

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