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<!--
$Header: /cvsroot/pgsql/doc/src/sgml/ref/alter_sequence.sgml,v 1.5 2003/09/22 00:16:57 petere Exp $
PostgreSQL documentation
-->
<refentry id="SQL-ALTERSEQUENCE">
<refmeta>
<refentrytitle id="SQL-ALTERSEQUENCE-TITLE">ALTER SEQUENCE</refentrytitle>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
<refnamediv>
<refname>
ALTER SEQUENCE
</refname>
<refpurpose>
alter the definition of a sequence generator
</refpurpose>
</refnamediv>
<indexterm zone="sql-altersequence">
<primary>ALTER SEQUENCE</primary>
</indexterm>
<refsynopsisdiv>
<synopsis>
ALTER SEQUENCE <replaceable class="parameter">name</replaceable> [ INCREMENT [ BY ] <replaceable class="parameter">increment</replaceable> ]
[ MINVALUE <replaceable class="parameter">minvalue</replaceable> | NO MINVALUE ] [ MAXVALUE <replaceable class="parameter">maxvalue</replaceable> | NO MAXVALUE ]
[ RESTART [ WITH ] <replaceable class="parameter">start</replaceable> ] [ CACHE <replaceable class="parameter">cache</replaceable> ] [ [ NO ] CYCLE ]
</synopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>
<command>ALTER SEQUENCE</command> changes the parameters of an existing
sequence generator. Any parameter not specifically set in the
<command>ALTER SEQUENCE</command> command retains its prior setting.
</para>
</refsect1>
<refsect1>
<title>Parameters</title>
<para>
<variablelist>
<varlistentry>
<term><replaceable class="parameter">name</replaceable></term>
<listitem>
<para>
The name (optionally schema-qualified) of a sequence to be altered.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">increment</replaceable></term>
<listitem>
<para>
The
<option>INCREMENT BY <replaceable class="parameter">increment</replaceable></option>
clause is optional. A positive value will make an
ascending sequence, a negative one a descending sequence.
If unspecified, the old increment value will be maintained.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">minvalue</replaceable></term>
<term>NO MINVALUE</term>
<listitem>
<para>
The optional clause <option>MINVALUE
<replaceable class="parameter">minvalue</replaceable></option>
determines the minimum value
a sequence can generate. If <option>NO MINVALUE</option> is specified,
the defaults of 1 and -2^63-1 for ascending and descending sequences, respectively, will be used. If neither option is specified, the current minimum
value will be maintained.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">maxvalue</replaceable></term>
<term>NO MAXVALUE</term>
<listitem>
<para>
The optional clause <option>MAXVALUE
<replaceable class="parameter">maxvalue</replaceable></option>
determines the maximum value for the sequence. If
<option>NO MAXVALUE</option> is specified, the defaults are 2^63-1 and -1 for
ascending and descending sequences, respectively, will be used. If
neither option is specified, the current maximum value will be
maintained.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">start</replaceable></term>
<listitem>
<para>
The optional <option>RESTART WITH
<replaceable class="parameter">start</replaceable></option>
clause changes the current value of the sequence.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">cache</replaceable></term>
<listitem>
<para>
The <option>CACHE <replaceable class="parameter">cache</replaceable></option> option
enables sequence numbers to be preallocated
and stored in memory for faster access. The minimum
value is 1 (only one value can be generated at a time, i.e., no cache).
If unspecified, the old cache value will be maintained.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>CYCLE</term>
<listitem>
<para>
The optional <option>CYCLE</option> keyword may be used to enable
the sequence to wrap around when the
<replaceable class="parameter">maxvalue</replaceable> or
<replaceable class="parameter">minvalue</replaceable> has been
reached by
an ascending or descending sequence respectively. If the limit is
reached, the next number generated will be the
<replaceable class="parameter">minvalue</replaceable> or
<replaceable class="parameter">maxvalue</replaceable>,
respectively.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>NO CYCLE</term>
<listitem>
<para>
If the optional <option>NO CYCLE</option> keyword is specified, any
calls to <function>nextval</function> after the sequence has reached
its maximum value will return an error. If neither
<option>CYCLE</option> or <option>NO CYCLE</option> are specified,
the old cycle behaviour will be maintained.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1>
<title>Examples</title>
<para>
Restart a sequence called <literal>serial</literal>, at 105:
</para>
<programlisting>
ALTER SEQUENCE serial RESTART WITH 105;
</programlisting>
</refsect1>
<refsect1>
<title>Notes</title>
<para>
To avoid blocking of concurrent transactions that obtain numbers from the
same sequence, <command>ALTER SEQUENCE</command> is never rolled back;
the changes take effect immediately and are not reversible.
</para>
<para>
<command>ALTER SEQUENCE</command> will not immediately affect
<literal>nextval</> results in backends,
other than the current one, that have preallocated (cached) sequence
values. They will use up all cached values prior to noticing the changed
sequence parameters. The current backend will be affected immediately.
</para>
</refsect1>
<refsect1>
<title>
Compatibility
</title>
<refsect2>
<title>
SQL99
</title>
<para>
<command>ALTER SEQUENCE</command> is a <productname>PostgreSQL</productname>
language extension.
There is no <command>ALTER SEQUENCE</command> statement
in <acronym>SQL99</acronym>.
</para>
</refsect2>
</refsect1>
</refentry>
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