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| $PostgreSQL: pgsql/doc/src/sgml/ref/alter_sequence.sgml,v 1.15 2006/09/16 00:30:16 momjian Exp $ |
| PostgreSQL documentation |
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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> |
| change 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 ] |
| [ OWNED BY { <replaceable class="parameter">table</replaceable>.<replaceable class="parameter">column</replaceable> | NONE } ] |
| ALTER SEQUENCE <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</>. |
| To change a sequence's schema, you must also have <literal>CREATE</> |
| privilege on the new schema. |
| </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><literal>CYCLE</literal></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><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>OWNED BY</literal> <replaceable class="parameter">table</replaceable>.<replaceable class="parameter">column</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</>. |
| </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>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>'s effects on the sequence |
| generation parameters are never rolled back; |
| those changes take effect immediately and are not reversible. However, |
| the <literal>OWNED BY</> and <literal>SET SCHEMA</> clauses are ordinary |
| catalog updates and can be rolled back. |
| </para> |
| |
| <para> |
| <command>ALTER SEQUENCE</command> will not immediately affect |
| <function>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 generation parameters. The current backend will be affected |
| immediately. |
| </para> |
| |
| <para> |
| Some variants of <command>ALTER TABLE</command> can be used with |
| sequences as well; for example, to rename a sequence use <command>ALTER |
| TABLE RENAME</command>. |
| </para> |
| </refsect1> |
| |
| |
| <refsect1> |
| <title>Compatibility</title> |
| |
| <para> |
| <command>ALTER SEQUENCE</command> conforms to the <acronym>SQL</acronym> |
| standard, |
| except for the <literal>OWNED BY</> 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" endterm="sql-createsequence-title"></member> |
| <member><xref linkend="sql-dropsequence" endterm="sql-dropsequence-title"></member> |
| </simplelist> |
| </refsect1> |
| |
| </refentry> |