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BEGIN(7) PostgreSQL 12.3 Documentation 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 DEFERRABLEtransaction_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)
PostgreSQL 12.3 2020 BEGIN(7)
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