| | ALTER SEQUENCEName ALTER SEQUENCE
-- change the definition of a sequence generator
SynopsisALTER SEQUENCE name [ INCREMENT [ BY ] increment ]
[ MINVALUE minvalue | NO MINVALUE ] [ MAXVALUE maxvalue | NO MAXVALUE ]
[ RESTART [ WITH ] start ] [ CACHE cache ] [ [ NO ] CYCLE ]
Description ALTER SEQUENCE changes the parameters of an existing
sequence generator. Any parameter not specifically set in the
ALTER SEQUENCE command retains its prior setting.
Parameters - name
The name (optionally schema-qualified) of a sequence to be altered.
- 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
-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. 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.
- start
The optional clause RESTART WITH start changes the
current value of the sequence.
- cache
The clause CACHE cache enables
sequence numbers to be pre-allocated 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 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 nor NO
CYCLE is specified, the old cycle behaviour will be
maintained.
Examples Restart a sequence called serial, at 105:
ALTER SEQUENCE serial RESTART WITH 105;
Notes To avoid blocking of concurrent transactions that obtain numbers from the
same sequence, ALTER SEQUENCE is never rolled back;
the changes take effect immediately and are not reversible.
ALTER SEQUENCE will not immediately affect
nextval results in backends,
other than the current one, that have pre-allocated (cached) sequence
values. They will use up all cached values prior to noticing the changed
sequence parameters. The current backend will be affected immediately.
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