alter_sequence.7

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.\\" auto-generated by docbook2man-spec $Revision: 1.1.1.1 $
.TH "ALTER SEQUENCE" "" "2008-01-03" "SQL - Language Statements" "SQL Commands"
.SH NAME
ALTER SEQUENCE \- change the definition of a sequence generator

.SH SYNOPSIS
.sp
.nf
ALTER SEQUENCE \fIname\fR [ INCREMENT [ BY ] \fIincrement\fR ]
    [ MINVALUE \fIminvalue\fR | NO MINVALUE ] [ MAXVALUE \fImaxvalue\fR | NO MAXVALUE ]
    [ RESTART [ WITH ] \fIstart\fR ] [ CACHE \fIcache\fR ] [ [ NO ] CYCLE ]
    [ OWNED BY { \fItable\fR.\fIcolumn\fR | NONE } ]
ALTER SEQUENCE \fIname\fR SET SCHEMA \fInew_schema\fR
  
.sp
.fi
.SH "DESCRIPTION"
.PP
\fBALTER SEQUENCE\fR changes the parameters of an existing
sequence generator. Any parameters not specifically set in the
\fBALTER SEQUENCE\fR command retain their prior settings.
.PP
You must own the sequence to use \fBALTER SEQUENCE\fR.
To change a sequence's schema, you must also have CREATE
privilege on the new schema.
.SH "PARAMETERS"
.PP
.TP
\fB\fIname\fB\fR
The name (optionally schema-qualified) of a sequence to be altered.
.TP
\fB\fIincrement\fB\fR
The clause INCREMENT BY \fIincrement\fR 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.
.TP
\fB\fIminvalue\fB\fR
.TP
\fBNO MINVALUE\fR
The optional clause MINVALUE \fIminvalue\fR determines
the minimum value a sequence can generate. If NO
MINVALUE is specified, the defaults of 1 and
-263-1 for ascending and descending sequences,
respectively, will be used. If neither option is specified,
the current minimum value will be maintained.
.TP
\fB\fImaxvalue\fB\fR
.TP
\fBNO MAXVALUE\fR
The optional clause MAXVALUE \fImaxvalue\fR determines
the maximum value for the sequence. If NO
MAXVALUE is specified, the defaults are
263-1 and -1 for ascending and descending
sequences, respectively, will be used. If neither option is
specified, the current maximum value will be maintained.
.TP
\fB\fIstart\fB\fR
The optional clause RESTART WITH \fIstart\fR changes the
current value of the sequence.
.TP
\fB\fIcache\fB\fR
The clause CACHE \fIcache\fR 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.
.TP
\fBCYCLE\fR
The optional CYCLE key word may be used to enable
the sequence to wrap around when the
\fImaxvalue\fR or
\fIminvalue\fR has been
reached by
an ascending or descending sequence respectively. If the limit is
reached, the next number generated will be the
\fIminvalue\fR or
\fImaxvalue\fR,
respectively.
.TP
\fBNO CYCLE\fR
If the optional NO CYCLE key word is
specified, any calls to \fBnextval\fR after the
sequence has reached its maximum value will return an error.
If neither CYCLE or NO
CYCLE are specified, the old cycle behavior will be
maintained.
.TP
\fBOWNED BY \fItable\fB.\fIcolumn\fB\fR
.TP
\fBOWNED BY NONE\fR
The OWNED BY 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 OWNED BY NONE removes any existing
association, making the sequence ``free-standing''.
.TP
\fB\fInew_schema\fB\fR
The new schema for the sequence.
.PP
.SH "EXAMPLES"
.PP
Restart a sequence called serial, at 105:
.sp
.nf
ALTER SEQUENCE serial RESTART WITH 105;
.sp
.fi
.SH "NOTES"
.PP
To avoid blocking of concurrent transactions that obtain numbers from the
same sequence, \fBALTER SEQUENCE\fR's effects on the sequence
generation parameters are never rolled back;
those changes take effect immediately and are not reversible. However,
the OWNED BY and SET SCHEMA clauses are ordinary
catalog updates and can be rolled back.
.PP
\fBALTER SEQUENCE\fR will not immediately affect
\fBnextval\fR 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.
.PP
Some variants of \fBALTER TABLE\fR can be used with
sequences as well; for example, to rename a sequence use \fBALTER
TABLE RENAME\fR.
.SH "COMPATIBILITY"
.PP
\fBALTER SEQUENCE\fR conforms to the SQL
standard,
except for the OWNED BY and SET SCHEMA
clauses, which are PostgreSQL extensions.
.SH "SEE ALSO"
CREATE SEQUENCE [\fBcreate_sequence\fR(7)], DROP SEQUENCE [\fBdrop_sequence\fR(l)]