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<!--
doc/src/sgml/ref/start_transaction.sgml
PostgreSQL documentation
-->
<refentry id="sql-start-transaction">
<indexterm zone="sql-start-transaction">
<primary>START TRANSACTION</primary>
</indexterm>
<refmeta>
<refentrytitle>START TRANSACTION</refentrytitle>
<manvolnum>7</manvolnum>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
<refnamediv>
<refname>START TRANSACTION</refname>
<refpurpose>start a transaction block</refpurpose>
</refnamediv>
<refsynopsisdiv>
<synopsis>
START TRANSACTION [ <replaceable class="parameter">transaction_mode</replaceable> [, ...] ]
<phrase>where <replaceable class="parameter">transaction_mode</replaceable> is one of:</phrase>
ISOLATION LEVEL { SERIALIZABLE | REPEATABLE READ | READ COMMITTED | READ UNCOMMITTED }
READ WRITE | READ ONLY
[ NOT ] DEFERRABLE
</synopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>
This command begins a new transaction block. If the isolation level,
read/write mode, or deferrable mode is specified, the new transaction has those
characteristics, as if <link linkend="sql-set-transaction"><command>SET TRANSACTION</command></link> was executed. This is the same
as the <link linkend="sql-begin"><command>BEGIN</command></link> command.
</para>
</refsect1>
<refsect1>
<title>Parameters</title>
<para>
Refer to <xref linkend="sql-set-transaction"/> for information on the meaning
of the parameters to this statement.
</para>
</refsect1>
<refsect1>
<title>Compatibility</title>
<para>
In the standard, it is not necessary to issue <command>START TRANSACTION</command>
to start a transaction block: any SQL command implicitly begins a block.
<productname>PostgreSQL</productname>'s behavior can be seen as implicitly
issuing a <command>COMMIT</command> after each command that does not
follow <command>START TRANSACTION</command> (or <command>BEGIN</command>),
and it is therefore often called <quote>autocommit</quote>.
Other relational database systems might offer an autocommit feature
as a convenience.
</para>
<para>
The <literal>DEFERRABLE</literal>
<replaceable class="parameter">transaction_mode</replaceable>
is a <productname>PostgreSQL</productname> language extension.
</para>
<para>
The SQL standard requires commas between successive <replaceable
class="parameter">transaction_modes</replaceable>, but for historical
reasons <productname>PostgreSQL</productname> allows the commas to be
omitted.
</para>
<para>
See also the compatibility section of <xref linkend="sql-set-transaction"/>.
</para>
</refsect1>
<refsect1>
<title>See Also</title>
<simplelist type="inline">
<member><xref linkend="sql-begin"/></member>
<member><xref linkend="sql-commit"/></member>
<member><xref linkend="sql-rollback"/></member>
<member><xref linkend="sql-savepoint"/></member>
<member><xref linkend="sql-set-transaction"/></member>
</simplelist>
</refsect1>
</refentry>
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