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136 lines
3.7 KiB
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136 lines
3.7 KiB
Plaintext
<!--
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$PostgreSQL: pgsql/doc/src/sgml/ref/savepoint.sgml,v 1.5 2006/09/16 00:30:20 momjian Exp $
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PostgreSQL documentation
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-->
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<refentry id="SQL-SAVEPOINT">
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<refmeta>
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<refentrytitle id="SQL-SAVEPOINT-TITLE">SAVEPOINT</refentrytitle>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>SAVEPOINT</refname>
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<refpurpose>define a new savepoint within the current transaction</refpurpose>
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</refnamediv>
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<indexterm zone="sql-savepoint">
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<primary>SAVEPOINT</primary>
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</indexterm>
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<indexterm zone="sql-savepoint">
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<primary>savepoints</primary>
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<secondary>defining</secondary>
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</indexterm>
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<refsynopsisdiv>
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<synopsis>
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SAVEPOINT <replaceable>savepoint_name</replaceable>
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</synopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>
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<command>SAVEPOINT</command> establishes a new savepoint within
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the current transaction.
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</para>
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<para>
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A savepoint is a special mark inside a transaction that allows all commands
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that are executed after it was established to be rolled back, restoring
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the transaction state to what it was at the time of the savepoint.
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</para>
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</refsect1>
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<refsect1>
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<title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><replaceable>savepoint_name</replaceable></term>
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<listitem>
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<para>
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The name to give to the new savepoint.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>
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Use <xref linkend="SQL-ROLLBACK-TO" endterm="SQL-ROLLBACK-TO-TITLE"> to
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rollback to a savepoint. Use <xref linkend="SQL-RELEASE-SAVEPOINT"
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endterm="SQL-RELEASE-SAVEPOINT-TITLE"> to destroy a savepoint, keeping
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the effects of commands executed after it was established.
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</para>
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<para>
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Savepoints can only be established when inside a transaction block.
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There can be multiple savepoints defined within a transaction.
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</para>
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</refsect1>
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<refsect1>
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<title>Examples</title>
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<para>
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To establish a savepoint and later undo the effects of all commands executed
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after it was established:
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<programlisting>
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BEGIN;
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INSERT INTO table1 VALUES (1);
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SAVEPOINT my_savepoint;
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INSERT INTO table1 VALUES (2);
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ROLLBACK TO SAVEPOINT my_savepoint;
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INSERT INTO table1 VALUES (3);
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COMMIT;
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</programlisting>
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The above transaction will insert the values 1 and 3, but not 2.
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</para>
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<para>
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To establish and later destroy a savepoint:
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<programlisting>
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BEGIN;
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INSERT INTO table1 VALUES (3);
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SAVEPOINT my_savepoint;
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INSERT INTO table1 VALUES (4);
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RELEASE SAVEPOINT my_savepoint;
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COMMIT;
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</programlisting>
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The above transaction will insert both 3 and 4.
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</para>
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</refsect1>
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<refsect1>
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<title>Compatibility</title>
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<para>
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SQL requires a savepoint to be destroyed automatically when another
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savepoint with the same name is established. In
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<productname>PostgreSQL</>, the old savepoint is kept, though only the more
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recent one will be used when rolling back or releasing. (Releasing the
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newer savepoint will cause the older one to again become accessible to
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<command>ROLLBACK TO SAVEPOINT</> and <command>RELEASE SAVEPOINT</>.)
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Otherwise, <command>SAVEPOINT</command> is fully SQL conforming.
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</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<simplelist type="inline">
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<member><xref linkend="sql-begin" endterm="sql-begin-title"></member>
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<member><xref linkend="sql-commit" endterm="sql-commit-title"></member>
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<member><xref linkend="sql-release-savepoint" endterm="sql-release-savepoint-title"></member>
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<member><xref linkend="sql-rollback" endterm="sql-rollback-title"></member>
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<member><xref linkend="sql-rollback-to" endterm="sql-rollback-to-title"></member>
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</simplelist>
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</refsect1>
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</refentry>
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