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><H1
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>BEGIN</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN66368"
></A
><H2
>Name</H2
>BEGIN -- start a transaction block</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN66373"
></A
><H2
>Synopsis</H2
><PRE
CLASS="SYNOPSIS"
>BEGIN [ WORK | TRANSACTION ] [ <TT
CLASS="REPLACEABLE"
><I
>transaction_mode</I
></TT
> [, ...] ]
<SPAN
CLASS="phrase"
><SPAN
CLASS="PHRASE"
>where <TT
CLASS="REPLACEABLE"
><I
>transaction_mode</I
></TT
> is one of:</SPAN
></SPAN
>
ISOLATION LEVEL { SERIALIZABLE | REPEATABLE READ | READ COMMITTED | READ UNCOMMITTED }
READ WRITE | READ ONLY
[ NOT ] DEFERRABLE</PRE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN66378"
></A
><H2
>Description</H2
><P
> <TT
CLASS="COMMAND"
>BEGIN</TT
> initiates a transaction block, that is,
all statements after a <TT
CLASS="COMMAND"
>BEGIN</TT
> command will be
executed in a single transaction until an explicit <A
HREF="sql-commit.html"
>COMMIT</A
> or <A
HREF="sql-rollback.html"
>ROLLBACK</A
> is given.
By default (without <TT
CLASS="COMMAND"
>BEGIN</TT
>),
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> executes
transactions in <SPAN
CLASS="QUOTE"
>"autocommit"</SPAN
> 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).
</P
><P
> 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.
</P
><P
> If the isolation level, read/write mode, or deferrable mode is specified, the new
transaction has those characteristics, as if
<A
HREF="sql-set-transaction.html"
>SET TRANSACTION</A
>
was executed.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN66391"
></A
><H2
>Parameters</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>WORK</TT
><BR><TT
CLASS="LITERAL"
>TRANSACTION</TT
></DT
><DD
><P
> Optional key words. They have no effect.
</P
></DD
></DL
></DIV
><P
> Refer to <A
HREF="sql-set-transaction.html"
>SET TRANSACTION</A
> for information on the meaning
of the other parameters to this statement.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN66403"
></A
><H2
>Notes</H2
><P
> <A
HREF="sql-start-transaction.html"
>START TRANSACTION</A
> has the same functionality
as <TT
CLASS="COMMAND"
>BEGIN</TT
>.
</P
><P
> Use <A
HREF="sql-commit.html"
>COMMIT</A
> or
<A
HREF="sql-rollback.html"
>ROLLBACK</A
>
to terminate a transaction block.
</P
><P
> Issuing <TT
CLASS="COMMAND"
>BEGIN</TT
> 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 <A
HREF="sql-savepoint.html"
>SAVEPOINT</A
>).
</P
><P
> For reasons of backwards compatibility, the commas between successive
<TT
CLASS="REPLACEABLE"
><I
>transaction_modes</I
></TT
> can be
omitted.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN66416"
></A
><H2
>Examples</H2
><P
> To begin a transaction block:
</P><PRE
CLASS="PROGRAMLISTING"
>BEGIN;</PRE
><P></P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN66420"
></A
><H2
>Compatibility</H2
><P
> <TT
CLASS="COMMAND"
>BEGIN</TT
> is a <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>
language extension. It is equivalent to the SQL-standard command
<A
HREF="sql-start-transaction.html"
>START TRANSACTION</A
>, whose reference page
contains additional compatibility information.
</P
><P
> The <TT
CLASS="LITERAL"
>DEFERRABLE</TT
>
<TT
CLASS="REPLACEABLE"
><I
>transaction_mode</I
></TT
>
is a <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> language extension.
</P
><P
> Incidentally, the <TT
CLASS="LITERAL"
>BEGIN</TT
> 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.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN66432"
></A
><H2
>See Also</H2
><A
HREF="sql-commit.html"
>COMMIT</A
>, <A
HREF="sql-rollback.html"
>ROLLBACK</A
>, <A
HREF="sql-start-transaction.html"
>START TRANSACTION</A
>, <A
HREF="sql-savepoint.html"
>SAVEPOINT</A
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