begin(7)

1BEGIN(7)                         SQL Commands                         BEGIN(7)
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NAME

6       BEGIN - start a transaction block
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SYNOPSIS

10       BEGIN [ WORK | TRANSACTION ] [ transaction_mode [, ...] ]
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12       where transaction_mode is one of:
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14           ISOLATION LEVEL { SERIALIZABLE | REPEATABLE READ | READ COMMITTED | READ UNCOMMITTED }
15           READ WRITE | READ ONLY
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DESCRIPTION

19       BEGIN  initiates  a  transaction block, that is, all statements after a
20       BEGIN command will  be  executed  in  a  single  transaction  until  an
21       explicit  COMMIT  [commit(7)]  or  ROLLBACK [rollback(7)] is given.  By
22       default (without BEGIN), PostgreSQL executes transactions in ``autocom‐
23       mit''  mode, that is, each statement is executed in its own transaction
24       and a commit is implicitly performed at the end of  the  statement  (if
25       execution was successful, otherwise a rollback is done).
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27       Statements  are  executed  more quickly in a transaction block, because
28       transaction start/commit requires significant CPU  and  disk  activity.
29       Execution of multiple statements inside a transaction is also useful to
30       ensure consistency when making several related changes: other  sessions
31       will  be  unable  to  see  the  intermediate states wherein not all the
32       related updates have been done.
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34       If the isolation level or read/write mode is specified, the new  trans‐
35       action  has  those characteristics, as if SET TRANSACTION [set_transac‐
36       tion(7)] was executed.
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PARAMETERS

39       WORK
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41       TRANSACTION
42              Optional key words. They have no effect.
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44       Refer to SET TRANSACTION [set_transaction(7)] for  information  on  the
45       meaning of the other parameters to this statement.
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NOTES

48       START  TRANSACTION [start_transaction(7)] has the same functionality as
49       BEGIN.
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51       Use COMMIT [commit(7)] or ROLLBACK [rollback(7)] to terminate a  trans‐
52       action block.
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54       Issuing  BEGIN  when  already inside a transaction block will provoke a
55       warning message. The state of the transaction is not affected.  To nest
56       transactions  within a transaction block, use savepoints (see SAVEPOINT
57       [savepoint(7)]).
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59       For reasons of backwards compatibility, the commas  between  successive
60       transaction_modes can be omitted.
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EXAMPLES

63       To begin a transaction block:
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65       BEGIN;
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COMPATIBILITY

69       BEGIN  is a PostgreSQL language extension. It is equivalent to the SQL-
70       standard command START TRANSACTION [start_transaction(7)], whose refer‐
71       ence page contains additional compatibility information.
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73       Incidentally,  the  BEGIN  key  word is used for a different purpose in
74       embedded SQL. You are advised  to  be  careful  about  the  transaction
75       semantics when porting database applications.
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