BEGIN
SQL - Language Statements
BEGIN
start a transaction block
BEGIN
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 or 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
was executed.
Parameters
WORK
TRANSACTION
Optional key words. They have no effect.
Refer to for information on the meaning
of the other parameters to this statement.
Notes
has the same functionality
as BEGIN>.
Use or
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 ).
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
, 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