ALTER SEQUENCE

Changes the definition of a sequence generator.

Synopsis

ALTER SEQUENCE [ IF EXISTS ] <name>
     [ AS <data_type> ]
     [INCREMENT [ BY ] <increment>] 
     [MINVALUE <minvalue> | NO MINVALUE] 
     [MAXVALUE <maxvalue> | NO MAXVALUE] 
     [START [ WITH ] <start> ]
     [RESTART [ [ WITH ] <restart>] ]
     [CACHE <cache>] [[ NO ] CYCLE] 
     [OWNED BY {<table_name.column_name> | NONE}]

ALTER SEQUENCE [ IF EXISTS ] <name> OWNER TO { <new_owner> | CURRENT_USER | SESSION_USER }

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. Greenplum Database issues a notice in this case.
data_type
The optional clause AS data_type changes the data type of the sequence. Valid types are smallint, integer, and bigint.

Changing the data type automatically changes the minimum and maximum values of the sequence if and only if the previous minimum and maximum values were the minimum or maximum value of the old data type (in other words, if the sequence had been created using NO MINVALUE or NO MAXVALUE, implicitly or explicitly). Otherwise, the minimum and maximum values are preserved, unless new values are given as part of the same command. If the minimum and maximum values do not fit into the new data type, Greenplum Database generates an error.

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 the minimum value of the data type 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 of the maximum value of the data type 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 the setval(sequence, start_val, is_called) function with is_called = false. The specified value will be returned by the next call of the nextval(sequence) function. Writing RESTART with no restart value is equivalent to supplying the start value that was recorded by CREATE SEQUENCE or last set by ALTER SEQUENCE START WITH.
In contrast to a setval() call, a RESTART operation on a sequence is transactional and blocks concurrent transactions from obtaining numbers from the same sequence. If that’s not the desired mode of operation, setval() should be used
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.
Note

When operating with a cache of sequence numbers (cache > 1), Greenplum Database may discard some cached sequence values. If you require consecutive values, you must explicitly set CACHE 1 when you create or alter the sequence.

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 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_name.column_name
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 table column association.
new_owner
The user name of the new owner of the sequence.
new_name
The new name for the sequence.
new_schema
The new schema for the sequence.

Notes

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.

ALTER SEQUENCE blocks concurrent nextval() and setval() calls.

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 AS, 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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