Changes the definition of a sequence generator.
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> RENAME TO new\_name
ALTER SEQUENCE <name> SET SCHEMA <new_schema>
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. Note that superusers have all these privileges automatically.
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 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 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.
RESTART WITH
start changes the current value of the sequence. Altering the sequence in this manner is equivalent to calling the
setval(sequence, start_val, is_called)
function with
is_called = false
. The first
nextval()
call after you alter the sequence start value does not increment the sequence and returns start.
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
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. If the limit is reached, the next number generated will be the respective minvalue or maxvalue.
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
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 table column association.
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
, RENAME TO
, and SET SCHEMA
clauses are ordinary catalog updates and can be rolled back.
ALTER SEQUENCE
will not immediately affect nextval()
results in sessions, 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 session 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
.
Restart a sequence called serial
at 105
:
ALTER SEQUENCE serial RESTART WITH 105;
ALTER SEQUENCE
conforms to the SQL standard, except for the OWNED BY
, RENAME TO
, and SET SCHEMA
clauses, which are Greenplum Database extensions.
CREATE SEQUENCE, DROP SEQUENCE, ALTER TABLE
Parent topic: SQL Command Reference