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<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>
  <refsynopsisdivinfo>
   <date>1999-07-20</date>
  </refsynopsisdivinfo>
  <synopsis>
ALTER SEQUENCE <replaceable class="parameter">seqname</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>
  
  <refsect2 id="R2-SQL-ALTERSEQUENCE-1">
   <refsect2info>
    <date>1998-09-11</date>
   </refsect2info>
   <title>
    Inputs
   </title>
   <para>

    <variablelist>
     <varlistentry>
      <term><replaceable class="parameter">seqname</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>
	 clause</option> enables the sequence to re-begin anywhere.
       </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>
  </refsect2>

  <refsect2 id="R2-SQL-ALTERSEQUENCE-2">
   <refsect2info>
    <date>1998-09-11</date>
   </refsect2info>
   <title>
    Outputs
   </title>
   <para>

    <variablelist>
     <varlistentry>
      <term><computeroutput>
ALTER SEQUENCE
       </computeroutput></term>
      <listitem>
       <para>
	Message returned if the command is successful.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><computeroutput>
ERROR:  AlterSequence: MINVALUE (<replaceable class="parameter">start</replaceable>) can't be >= MAXVALUE (<replaceable class="parameter">max</replaceable>)
       </computeroutput></term>
      <listitem>
       <para>
	If the specified starting value is out of range.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><computeroutput>
ERROR:  AlterSequence: START value (<replaceable class="parameter">start</replaceable>) can't be < MINVALUE (<replaceable class="parameter">min</replaceable>)
       </computeroutput></term>
      <listitem>
       <para>
	If the specified starting value is out of range.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><computeroutput>
ERROR:  AlterSequence: MINVALUE (<replaceable class="parameter">min</replaceable>) can't be >= MAXVALUE (<replaceable class="parameter">max</replaceable>)
       </computeroutput></term>
      <listitem>
       <para>
	If the minimum and maximum values are inconsistent.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </refsect2>
 </refsynopsisdiv>

 <refsect1 id="R1-SQL-ALTERSEQUENCE-1">
  <title>
   Description
  </title>

  <para>
   See <xref linkend="SQL-CREATESEQUENCE"> for limitations, and uses
   of sequences.
  </para>
 </refsect1>

 <refsect1 id="R1-SQL-ALTERSEQUENCE-2">
  <title>
   Usage
  </title>
  <para>
   Restart a sequence called <literal>serial</literal>, at 105:
  </para>
  <programlisting>
ALTER SEQUENCE serial RESTART WITH 105;
  </programlisting>
 </refsect1>

 <refsect1 id="R1-SQL-ALTERSEQUENCE-5">
  <title>
   Notes
  </title>
  <para>
   To avoid blocking of concurrent transactions that obtain numbers from the same
   sequence, a nextval operation is never rolled back; that is, once a value has 
   been fetched it is considered used, even if the transaction that did the nextval
   later aborts. This means that aborted transactions may leave unused "holes" in
   the sequence of assigned values. setval operations are never rolled back, either.
  </para>
  <para>
   <command>ALTER SEQUENCE</command> will not immediately affect backends, other than the
   current one, which have cached sequence values. They must use up all cached values
   prior to noticing the changed sequence parameters.  The current backend will be 
   immediatly affected.
  </para>
 </refsect1>


 <refsect1 id="R1-SQL-ALTERSEQUENCE-3">
  <title>
   Compatibility
  </title>

  <refsect2 id="R2-SQL-ALTERSEQUENCE-4">
   <refsect2info>
    <date>2003-03-02</date>
   </refsect2info>
   <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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