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)