Changes the definition of a sequence generator.
Synopsis
ALTER SEQUENCE [ IF EXISTS ] <name> [INCREMENT [ BY ] <increment>]
[MINVALUE <minvalue> | NO MINVALUE]
[MAXVALUE <maxvalue> | NO MAXVALUE]
[START [ WITH ] <start> ]
[RESTART [ [ WITH ] <restart>] ]
[CACHE <cache>] [[ NO ] CYCLE]
[OWNED BY {<table.column> | NONE}]
ALTER SEQUENCE [ IF EXISTS ] <name> OWNER TO <new_owner>
ALTER SEQUENCE [ IF EXISTS ] <name> RENAME TO <new_name>
ALTER SEQUENCE [ IF EXISTS ] <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. Note that superusers have all these privileges automatically.
To alter the owner, you must be a direct or indirect member of the new owning role, and that role must have CREATE
privilege on the sequence's schema. (These restrictions enforce that altering the owner does not do anything you could not do by dropping and recreating the sequence. However, a superuser can alter ownership of any sequence anyway.)
Parameters
- name
- The name (optionally schema-qualified) of a sequence to be altered.
- IF EXISTS
- Do not throw an error if the sequence does not exist. A notice is issued in this case.
- 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. IfNO 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. IfNO 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 START WITH start changes the recorded start value of the sequence. This has no effect on the current sequence value; it simply sets the value that future
ALTER SEQUENCE RESTART
commands will use. - restart
- The optional clause
RESTART [ WITH restart ]
changes the current value of the sequence. This is equivalent to calling thesetval(sequence, start\_val, is\_called)
function withis\_called = false
. The specified value will be returned by the next call of thenextval(sequence)
function. WritingRESTART
with no restart value is equivalent to supplying the start value that was recorded byCREATE SEQUENCE
or last set byALTER SEQUENCE START WITH
. - new_owner
- The user name of the new owner 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. If the limit is reached, the next number generated will be the respective minvalue or maxvalue. - NO CYCLE
- If the optional
NO CYCLE
key word is specified, any calls tonextval()
after the sequence has reached its maximum value will return an error. If neitherCYCLE
orNO 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. SpecifyingOWNED BY NONE
removes any existing table column association. - new_name
- The new name for the sequence.
- new_schema
- The new schema for the sequence.
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
, OWNER TO
, 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.
For historical reasons, ALTER TABLE
can be used with sequences too; but the only variants of ALTER TABLE
that are allowed with sequences are equivalent to the forms shown above.
Examples
Restart a sequence called serial
at 105
:
ALTER SEQUENCE serial RESTART WITH 105;
Compatibility
ALTER SEQUENCE
conforms to the SQL standard, except for the START WITH
, OWNED BY
, OWNER TO
, RENAME TO
, and SET SCHEMA
clauses, which are Greenplum Database extensions.
See Also
CREATE SEQUENCE, DROP SEQUENCE, ALTER TABLE
Parent topic: SQL Commands
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