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 transaction until an
       explicit COMMIT [commit(7)] or ROLLBACK [rollback(7)] is given.  By default (without BEGIN), PostgreSQL executes transactions in ``autocom-
       mit'' 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 ses-
       sions 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 TRANSACTION  [set_transac-
       tion(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_transaction(7)], whose ref-
       erence 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                                           2010-05-14                                                            BEGIN(7)