<!--
doc/src/sgml/ref/alter_sequence.sgml
PostgreSQL documentation
-->

<refentry id="sql-altersequence">
 <indexterm zone="sql-altersequence">
  <primary>ALTER SEQUENCE</primary>
 </indexterm>

 <refmeta>
  <refentrytitle>ALTER SEQUENCE</refentrytitle>
  <manvolnum>7</manvolnum>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>ALTER SEQUENCE</refname>
  <refpurpose>
   change the definition of a sequence generator
  </refpurpose>
 </refnamediv>

 <refsynopsisdiv>
<synopsis>
ALTER SEQUENCE [ IF EXISTS ] <replaceable class="parameter">name</replaceable>
    [ AS <replaceable class="parameter">data_type</replaceable> ]
    [ INCREMENT [ BY ] <replaceable class="parameter">increment</replaceable> ]
    [ MINVALUE <replaceable class="parameter">minvalue</replaceable> | NO MINVALUE ] [ MAXVALUE <replaceable class="parameter">maxvalue</replaceable> | NO MAXVALUE ]
    [ START [ WITH ] <replaceable class="parameter">start</replaceable> ]
    [ RESTART [ [ WITH ] <replaceable class="parameter">restart</replaceable> ] ]
    [ CACHE <replaceable class="parameter">cache</replaceable> ] [ [ NO ] CYCLE ]
    [ OWNED BY { <replaceable class="parameter">table_name</replaceable>.<replaceable class="parameter">column_name</replaceable> | NONE } ]
ALTER SEQUENCE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> SET { LOGGED | UNLOGGED }
ALTER SEQUENCE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> OWNER TO { <replaceable class="parameter">new_owner</replaceable> | CURRENT_ROLE | CURRENT_USER | SESSION_USER }
ALTER SEQUENCE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> RENAME TO <replaceable class="parameter">new_name</replaceable>
ALTER SEQUENCE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> SET SCHEMA <replaceable class="parameter">new_schema</replaceable>
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <command>ALTER SEQUENCE</command> changes the parameters of an existing
   sequence generator.  Any parameters not specifically set in the
   <command>ALTER SEQUENCE</command> command retain their prior settings.
  </para>

  <para>
   You must own the sequence to use <command>ALTER SEQUENCE</command>.
   To change a sequence's schema, you must also have <literal>CREATE</literal>
   privilege on the new schema.
   To alter the owner, you must be able to <literal>SET ROLE</literal> to the
   new owning role, and that role must have <literal>CREATE</literal>
   privilege on the sequence's schema.
   (These restrictions enforce that altering the owner
   doesn't do anything you couldn't do by dropping and recreating the sequence.
   However, a superuser can alter ownership of any sequence anyway.)
  </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><literal>IF EXISTS</literal></term>
      <listitem>
       <para>
        Do not throw an error if the sequence does not exist. A notice is issued
        in this case.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">data_type</replaceable></term>
      <listitem>
       <para>
        The optional
        clause <literal>AS <replaceable class="parameter">data_type</replaceable></literal>
        changes the data type of the sequence.  Valid types are
        <literal>smallint</literal>, <literal>integer</literal>,
        and <literal>bigint</literal>.
       </para>

       <para>
        Changing the data type automatically changes the minimum and maximum
        values of the sequence if and only if the previous minimum and maximum
        values were the minimum or maximum value of the old data type (in
        other words, if the sequence had been created using <literal>NO
        MINVALUE</literal> or <literal>NO MAXVALUE</literal>, implicitly or
        explicitly).  Otherwise, the minimum and maximum values are preserved,
        unless new values are given as part of the same command.  If the
        minimum and maximum values do not fit into the new data type, an error
        will be generated.
       </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
        the minimum value of the data type 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 of
        the maximum value of the data type 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>START WITH <replaceable
        class="parameter">start</replaceable></literal> changes the
        recorded start value of the sequence.  This has no effect on the
        <emphasis>current</emphasis> sequence value; it simply sets the value
        that future <command>ALTER SEQUENCE RESTART</command> commands will use.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">restart</replaceable></term>
      <listitem>
       <para>
        The optional clause <literal>RESTART [ WITH <replaceable
        class="parameter">restart</replaceable> ]</literal> changes the
        current value of the sequence.  This is similar to calling the
        <function>setval</function> function with <literal>is_called</literal> =
        <literal>false</literal>: the specified value will be returned by the
        <emphasis>next</emphasis> call of <function>nextval</function>.
        Writing <literal>RESTART</literal> with no <replaceable
        class="parameter">restart</replaceable> value is equivalent to supplying
        the start value that was recorded by <command>CREATE SEQUENCE</command>
        or last set by <command>ALTER SEQUENCE START WITH</command>.
       </para>

       <para>
        In contrast to a <function>setval</function> call,
        a <literal>RESTART</literal> operation on a sequence is transactional
        and blocks concurrent transactions from obtaining numbers from the
        same sequence. If that's not the desired mode of
        operation, <function>setval</function> should be used.
       </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><literal>CYCLE</literal></term>
      <listitem>
       <para>
        The optional <literal>CYCLE</literal> key word can 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><literal>NO CYCLE</literal></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 behavior will be
        maintained.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>SET { LOGGED | UNLOGGED }</literal></term>
      <listitem>
       <para>
        This form changes the sequence from unlogged to logged or vice-versa
        (see <xref linkend="sql-createsequence"/>).  It cannot be applied to a
        temporary sequence.
       </para>
      </listitem>
     </varlistentry>

   <varlistentry>
    <term><literal>OWNED BY</literal> <replaceable class="parameter">table_name</replaceable>.<replaceable class="parameter">column_name</replaceable></term>
    <term><literal>OWNED BY NONE</literal></term>
    <listitem>
     <para>
      The <literal>OWNED BY</literal> option causes the sequence to be
      associated with a specific table column, such that if that column
      (or its whole table) is dropped, the sequence will be automatically
      dropped as well.  If specified, this association replaces any
      previously specified association for the sequence.  The specified
      table must have the same owner and be in the same schema as the
      sequence.
      Specifying <literal>OWNED BY NONE</literal> removes any existing
      association, making the sequence <quote>free-standing</quote>.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">new_owner</replaceable></term>
    <listitem>
     <para>
      The user name of the new owner of the sequence.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">new_name</replaceable></term>
    <listitem>
     <para>
      The new name for the sequence.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">new_schema</replaceable></term>
    <listitem>
     <para>
      The new schema for the sequence.
     </para>
    </listitem>
   </varlistentry>

    </variablelist>
   </para>
  </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   <command>ALTER SEQUENCE</command> will not immediately affect
   <function>nextval</function> 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 generation parameters.  The current backend will be affected
   immediately.
  </para>

  <para>
   <command>ALTER SEQUENCE</command> does not affect the <function>currval</function>
   status for the sequence.  (Before <productname>PostgreSQL</productname>
   8.3, it sometimes did.)
  </para>

  <para>
   <command>ALTER SEQUENCE</command> blocks
   concurrent <function>nextval</function>, <function>currval</function>,
   <function>lastval</function>, and <command>setval</command> calls.
  </para>

  <para>
   For historical reasons, <command>ALTER TABLE</command> can be used with
   sequences too; but the only variants of <command>ALTER TABLE</command>
   that are allowed with sequences are equivalent to the forms shown above.
  </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>Compatibility</title>

  <para>
   <command>ALTER SEQUENCE</command> conforms to the <acronym>SQL</acronym>
   standard, except for the <literal>AS</literal>, <literal>START WITH</literal>,
   <literal>OWNED BY</literal>, <literal>OWNER TO</literal>, <literal>RENAME TO</literal>, and
   <literal>SET SCHEMA</literal> clauses, which are
   <productname>PostgreSQL</productname> extensions.
  </para>
 </refsect1>

 <refsect1>
  <title>See Also</title>

  <simplelist type="inline">
   <member><xref linkend="sql-createsequence"/></member>
   <member><xref linkend="sql-dropsequence"/></member>
  </simplelist>
 </refsect1>

</refentry>
