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<!--
doc/src/sgml/ref/savepoint.sgml
PostgreSQL documentation
-->
<refentry id="sql-savepoint">
<indexterm zone="sql-savepoint">
<primary>SAVEPOINT</primary>
</indexterm>
<indexterm zone="sql-savepoint">
<primary>savepoints</primary>
<secondary>defining</secondary>
</indexterm>
<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>
<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. If savepoints with the
same name already exist, they will be inaccessible until newer
identically-named savepoints are released.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Notes</title>
<para>
Use <link linkend="sql-rollback-to"><command>ROLLBACK TO</command></link> to
rollback to a savepoint. Use <link linkend="sql-release-savepoint"><command>RELEASE SAVEPOINT</command></link>
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>
<para>
To use a single savepoint name:
<programlisting>
BEGIN;
INSERT INTO table1 VALUES (1);
SAVEPOINT my_savepoint;
INSERT INTO table1 VALUES (2);
SAVEPOINT my_savepoint;
INSERT INTO table1 VALUES (3);
-- rollback to the second savepoint
ROLLBACK TO SAVEPOINT my_savepoint;
SELECT * FROM table1; -- shows rows 1 and 2
-- release the second savepoint
RELEASE SAVEPOINT my_savepoint;
-- rollback to the first savepoint
ROLLBACK TO SAVEPOINT my_savepoint;
SELECT * FROM table1; -- shows only row 1
COMMIT;
</programlisting>
The above transaction shows row 3 being rolled back first, then row 2.
</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</productname>, 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</command> will cause the older one
to again become accessible to <command>ROLLBACK TO SAVEPOINT</command> and
<command>RELEASE SAVEPOINT</command>.) 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>
|
