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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>BEGIN</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="sql-analyze.html" title="ANALYZE" /><link rel="next" href="sql-call.html" title="CALL" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">BEGIN</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="sql-analyze.html" title="ANALYZE">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><th width="60%" align="center">SQL Commands</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="sql-call.html" title="CALL">Next</a></td></tr></table><hr></hr></div><div class="refentry" id="SQL-BEGIN"><div class="titlepage"></div><a id="id-1.9.3.47.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle">BEGIN</span></h2><p>BEGIN — start a transaction block</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><pre class="synopsis">
BEGIN [ WORK | TRANSACTION ] [ <em class="replaceable"><code>transaction_mode</code></em> [, ...] ]
<span class="phrase">where <em class="replaceable"><code>transaction_mode</code></em> is one of:</span>
ISOLATION LEVEL { SERIALIZABLE | REPEATABLE READ | READ COMMITTED | READ UNCOMMITTED }
READ WRITE | READ ONLY
[ NOT ] DEFERRABLE
</pre></div><div class="refsect1" id="id-1.9.3.47.5"><h2>Description</h2><p>
<code class="command">BEGIN</code> initiates a transaction block, that is,
all statements after a <code class="command">BEGIN</code> command will be
executed in a single transaction until an explicit <a class="xref" href="sql-commit.html" title="COMMIT"><span class="refentrytitle">COMMIT</span></a> or <a class="xref" href="sql-rollback.html" title="ROLLBACK"><span class="refentrytitle">ROLLBACK</span></a> is given.
By default (without <code class="command">BEGIN</code>),
<span class="productname">PostgreSQL</span> executes
transactions in <span class="quote">“<span class="quote">autocommit</span>”</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 class="xref" href="sql-set-transaction.html" title="SET TRANSACTION"><span class="refentrytitle">SET TRANSACTION</span></a>
was executed.
</p></div><div class="refsect1" id="id-1.9.3.47.6"><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">WORK</code><br /></span><span class="term"><code class="literal">TRANSACTION</code></span></dt><dd><p>
Optional key words. They have no effect.
</p></dd></dl></div><p>
Refer to <a class="xref" href="sql-set-transaction.html" title="SET TRANSACTION"><span class="refentrytitle">SET TRANSACTION</span></a> for information on the meaning
of the other parameters to this statement.
</p></div><div class="refsect1" id="id-1.9.3.47.7"><h2>Notes</h2><p>
<a class="xref" href="sql-start-transaction.html" title="START TRANSACTION"><span class="refentrytitle">START TRANSACTION</span></a> has the same functionality
as <code class="command">BEGIN</code>.
</p><p>
Use <a class="xref" href="sql-commit.html" title="COMMIT"><span class="refentrytitle">COMMIT</span></a> or
<a class="xref" href="sql-rollback.html" title="ROLLBACK"><span class="refentrytitle">ROLLBACK</span></a>
to terminate a transaction block.
</p><p>
Issuing <code class="command">BEGIN</code> 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 class="xref" href="sql-savepoint.html" title="SAVEPOINT"><span class="refentrytitle">SAVEPOINT</span></a>).
</p><p>
For reasons of backwards compatibility, the commas between successive
<em class="replaceable"><code>transaction_modes</code></em> can be
omitted.
</p></div><div class="refsect1" id="id-1.9.3.47.8"><h2>Examples</h2><p>
To begin a transaction block:
</p><pre class="programlisting">
BEGIN;
</pre></div><div class="refsect1" id="id-1.9.3.47.9"><h2>Compatibility</h2><p>
<code class="command">BEGIN</code> is a <span class="productname">PostgreSQL</span>
language extension. It is equivalent to the SQL-standard command
<a class="xref" href="sql-start-transaction.html" title="START TRANSACTION"><span class="refentrytitle">START TRANSACTION</span></a>, whose reference page
contains additional compatibility information.
</p><p>
The <code class="literal">DEFERRABLE</code>
<em class="replaceable"><code>transaction_mode</code></em>
is a <span class="productname">PostgreSQL</span> language extension.
</p><p>
Incidentally, the <code class="literal">BEGIN</code> 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" id="id-1.9.3.47.10"><h2>See Also</h2><span class="simplelist"><a class="xref" href="sql-commit.html" title="COMMIT"><span class="refentrytitle">COMMIT</span></a>, <a class="xref" href="sql-rollback.html" title="ROLLBACK"><span class="refentrytitle">ROLLBACK</span></a>, <a class="xref" href="sql-start-transaction.html" title="START TRANSACTION"><span class="refentrytitle">START TRANSACTION</span></a>, <a class="xref" href="sql-savepoint.html" title="SAVEPOINT"><span class="refentrytitle">SAVEPOINT</span></a></span></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sql-analyze.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sql-commands.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sql-call.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">ANALYZE </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> CALL</td></tr></table></div></body></html>
