BEGIN(7)                                                  SQL Commands                                                  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


DESCRIPTION
       BEGIN  initiates a transaction block, that is, all statements after a BEGIN command will be executed in a single transac-
       tion until an explicit COMMIT [commit(7)] or ROLLBACK [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 or read/write mode is specified, the new transaction has those characteristics, as if SET TRANSAC-
       TION [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 [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.  To nest transactions within a transaction block, use savepoints (see SAVEPOINT [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_transac-
       tion(7)], whose reference page contains additional compatibility information.

       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(7)], START TRANSACTION [start_transaction(7)], SAVEPOINT [savepoint(7)]



SQL - Language Statements                                  2011-09-22                                                   BEGIN(7)