ALTER SEQUENCE

ALTER SEQUENCE

7

SQL - Language Statements

ALTER SEQUENCE

change the definition of a sequence generator

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

SET { LOGGED \| UNLOGGED } ALTER SEQUENCE \[ IF EXISTS \]

name

OWNER TO {

new\_owner

\| CURRENT\_ROLE \| 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. To alter the owner, you must also 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 doesn\'t do anything you couldn\'t 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.

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, an error will be
    generated.

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 similar to calling the `setval`
    function with `is_called` = `false`: the specified value will be
    returned by the *next* call of `nextval`. 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.

`CYCLE`

:   The optional `CYCLE` key word can 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.

`SET { LOGGED | UNLOGGED }`

:   This form changes the sequence from unlogged to logged or vice-versa
    (see [???](#sql-createsequence)). It cannot be applied to a
    temporary sequence.

`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 association, making the
    sequence "free-standing".

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` does not affect the `currval` status for the sequence.
(Before PostgreSQL 8.3, it sometimes did.)

`ALTER SEQUENCE` blocks concurrent `nextval`, `currval`, `lastval`, 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 PostgreSQL extensions.

See Also
========
