savepoint.sgml

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/savepoint.sgml,v 1.4 2005/01/06 20:53:34 tgl Exp $
PostgreSQL documentation
-->

<refentry id="SQL-SAVEPOINT">
 <refmeta>
  <refentrytitle id="SQL-SAVEPOINT-TITLE">SAVEPOINT</refentrytitle>
  <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" endterm="SQL-ROLLBACK-TO-TITLE"> to
   rollback to a savepoint.  Use <xref linkend="SQL-RELEASE-SAVEPOINT"
   endterm="SQL-RELEASE-SAVEPOINT-TITLE"> 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 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" endterm="sql-begin-title"></member>
   <member><xref linkend="sql-commit" endterm="sql-commit-title"></member>
   <member><xref linkend="sql-release-savepoint" endterm="sql-release-savepoint-title"></member>
   <member><xref linkend="sql-rollback" endterm="sql-rollback-title"></member>
   <member><xref linkend="sql-rollback-to" endterm="sql-rollback-to-title"></member>
  </simplelist>
 </refsect1>
</refentry>

<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:nil
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
sgml-parent-document:nil
sgml-default-dtd-file:"../reference.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:"/usr/lib/sgml/catalog"
sgml-local-ecat-files:nil
End:
-->