<!--
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 <xref linkend="sql-set-transaction"> was executed. This is the same
   as the <xref linkend="sql-begin"> 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>
