ALTER SEQUENCE — change the definition of a sequence generator
ALTER SEQUENCE [ IF EXISTS ]name
[ ASdata_type
] [ INCREMENT [ BY ]increment
] [ MINVALUEminvalue
| NO MINVALUE ] [ MAXVALUEmaxvalue
| NO MAXVALUE ] [ START [ WITH ]start
] [ RESTART [ [ WITH ]restart
] ] [ CACHEcache
] [ [ 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 TOnew_name
ALTER SEQUENCE [ IF EXISTS ]name
SET SCHEMAnew_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.
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.)
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
changes the data type of the sequence. Valid types are
data_type
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
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.
increment
minvalue
NO MINVALUE
The optional clause MINVALUE
determines
the minimum value a sequence can generate. If minvalue
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
determines
the maximum value for the sequence. If maxvalue
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
changes the
recorded start value of the sequence. This has no effect on the
current sequence value; it simply sets the value
that future start
ALTER SEQUENCE RESTART
commands will use.
restart
The optional clause RESTART [ WITH
changes the
current value of the sequence. This is similar to calling the
restart
]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
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.
cache
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.
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.
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 LightDB
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.
Restart a sequence called serial
, at 105:
ALTER SEQUENCE serial RESTART WITH 105;
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
LightDB extensions.