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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 ]
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 -263-1 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 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.

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.

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 is never rolled back; the changes take effect immediately and are not reversible.

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 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 SET SCHEMA variant, which is a PostgreSQL extension.


 
 
  Published courtesy of The PostgreSQL Global Development Group Design by Interspire