PostgreSQL - SQL Language Reference

PostgreSQL Reference Manual - Volume 1 - SQL Language Reference
by The PostgreSQL Global Development Group
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ISBN 0954612027
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PostgreSQL Reference Manual
Volume 1

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12.14 ALTER SEQUENCE

Name

ALTER SEQUENCE --- change the definition of a sequence generator

Synopsis

ALTER SEQUENCE name [ INCREMENT [ BY ] increment ]
    [ MINVALUE minvalue | NO MINVALUE ] [ MAXVALUE maxvalue |
 NO MAXVALUE ]
    [ RESTART [ WITH ] start ] [ CACHE cache ] [ [ NO ] CYCLE ]
    [ OWNED BY { table.column | NONE } ]
ALTER SEQUENCE name SET SCHEMA new_schema

Description

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

You must own the sequence to use ALTER SEQUENCE. To change a sequence's schema, you must also have CREATE privilege on the new schema.

Parameters

name: The name (optionally schema-qualified) of a sequence to be altered.
increment: The clause INCREMENT BY increment 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.
minvalue
NO MINVALUE: The optional clause MINVALUE minvalue determines the minimum value a sequence can generate. If NO MINVALUE 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.
maxvalue
NO MAXVALUE: The optional clause MAXVALUE maxvalue determines the maximum value for the sequence. If NO MAXVALUE 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.
start: The optional clause RESTART WITH start changes the current value of the sequence.
cache: The clause CACHE cache 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.
CYCLE: The optional CYCLE key word may be used to enable the sequence to wrap around when the maxvalue or minvalue has been reached by an ascending or descending sequence respectively. If the limit is reached, the next number generated will be the minvalue or maxvalue, respectively.
NO CYCLE: If the optional NO CYCLE key word is specified, any calls to nextval 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.
OWNED BY table.column
OWNED BY NONE: 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”.
new_schema: The new schema for the sequence.

Examples

Restart a sequence called serial, at 105:

ALTER SEQUENCE serial RESTART WITH 105;

Notes

To avoid blocking of concurrent transactions that obtain numbers from the same sequence, ALTER SEQUENCE'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.

ALTER SEQUENCE will not immediately affect 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.

Some variants of ALTER TABLE can be used with sequences as well; for example, to rename a sequence use ALTER TABLE RENAME.

Compatibility

ALTER SEQUENCE conforms to the SQL standard, except for the OWNED BY and SET SCHEMA clauses, which are PostgreSQL extensions.