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<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/alter_sequence.sgml,v 1.7 2003/11/29 19:51:38 pgsql 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 clause <literal>INCREMENT BY <replaceable
class="parameter">increment</replaceable></literal> 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><literal>NO MINVALUE</literal></term>
<listitem>
<para>
The optional clause <literal>MINVALUE <replaceable
class="parameter">minvalue</replaceable></literal> determines
the minimum value a sequence can generate. If <literal>NO
MINVALUE</literal> is specified, the defaults of 1 and
-2<superscript>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><literal>NO MAXVALUE</literal></term>
<listitem>
<para>
The optional clause <literal>MAXVALUE <replaceable
class="parameter">maxvalue</replaceable></literal> determines
the maximum value for the sequence. If <literal>NO
MAXVALUE</literal> is specified, the defaults are
2<superscript>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 clause <literal>RESTART WITH <replaceable
class="parameter">start</replaceable></literal> changes the
current value of the sequence.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">cache</replaceable></term>
<listitem>
<para>
The clause <literal>CACHE <replaceable
class="parameter">cache</replaceable></literal> 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 <literal>CYCLE</literal> key word 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 <literal>NO CYCLE</literal> key word is
specified, any calls to <function>nextval</function> after the
sequence has reached its maximum value will return an error.
If neither <literal>CYCLE</literal> or <literal>NO
CYCLE</literal> 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:
<programlisting>
ALTER SEQUENCE serial RESTART WITH 105;
</programlisting>
</para>
</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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