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$PostgreSQL: pgsql/doc/src/sgml/ref/savepoint.sgml,v 1.8 2010/05/27 06:25:32 heikki Exp $
PostgreSQL documentation
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<refentry id="SQL-SAVEPOINT">
 <refmeta>
  <refentrytitle>SAVEPOINT</refentrytitle>
  <manvolnum>7</manvolnum>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>SAVEPOINT</refname>
  <refpurpose>define a new savepoint within the current transaction</refpurpose>
 </refnamediv>

 <indexterm zone="sql-savepoint">
  <primary>SAVEPOINT</primary>
 </indexterm>

 <indexterm zone="sql-savepoint">
  <primary>savepoints</primary>
  <secondary>defining</secondary>
 </indexterm>

 <refsynopsisdiv>
<synopsis>
SAVEPOINT <replaceable>savepoint_name</replaceable>
</synopsis>
 </refsynopsisdiv>
  
 <refsect1>
  <title>Description</title>

  <para>
   <command>SAVEPOINT</command> establishes a new savepoint within
   the current transaction.
  </para>

  <para>
   A savepoint is a special mark inside a transaction that allows all commands
   that are executed after it was established to be rolled back, restoring
   the transaction state to what it was at the time of the savepoint.
  </para>
 </refsect1>
  
 <refsect1>
  <title>Parameters</title>

  <variablelist>
   <varlistentry>
    <term><replaceable>savepoint_name</replaceable></term>
    <listitem>
     <para>
      The name to give to the new savepoint.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   Use <xref linkend="SQL-ROLLBACK-TO"> to
   rollback to a savepoint.  Use <xref linkend="SQL-RELEASE-SAVEPOINT">
   to destroy a savepoint, keeping
   the effects of commands executed after it was established.
  </para>

  <para>
   Savepoints can only be established when inside a transaction block.
   There can be multiple savepoints defined within a transaction.
  </para>
 </refsect1>

 <refsect1>
  <title>Examples</title>

  <para>
   To establish a savepoint and later undo the effects of all commands executed
   after it was established:
<programlisting>
BEGIN;
    INSERT INTO table1 VALUES (1);
    SAVEPOINT my_savepoint;
    INSERT INTO table1 VALUES (2);
    ROLLBACK TO SAVEPOINT my_savepoint;
    INSERT INTO table1 VALUES (3);
COMMIT;
</programlisting>
   The above transaction will insert the values 1 and 3, but not 2.
  </para>

  <para>
   To establish and later destroy a savepoint:
<programlisting>
BEGIN;
    INSERT INTO table1 VALUES (3);
    SAVEPOINT my_savepoint;
    INSERT INTO table1 VALUES (4);
    RELEASE SAVEPOINT my_savepoint;
COMMIT;
</programlisting>
   The above transaction will insert both 3 and 4.
  </para>
 </refsect1>

 <refsect1>
  <title>Compatibility</title>
  
  <para>
   SQL requires a savepoint to be destroyed automatically when another
   savepoint with the same name is established.  In
   <productname>PostgreSQL</>, the old savepoint is kept, though only the more
   recent one will be used when rolling back or releasing.  (Releasing the
   newer savepoint with <command>RELEASE SAVEPOINT</> will cause the older one
   to again become accessible to <command>ROLLBACK TO SAVEPOINT</> and
   <command>RELEASE SAVEPOINT</>.) Otherwise, <command>SAVEPOINT</command> is
   fully SQL conforming.
  </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-release-savepoint"></member>
   <member><xref linkend="sql-rollback"></member>
   <member><xref linkend="sql-rollback-to"></member>
  </simplelist>
 </refsect1>
</refentry>
