Man Linux: Main Page and Category List


       CREATE SEQUENCE - define a new sequence generator


       CREATE [ TEMPORARY | TEMP ] SEQUENCE name [ INCREMENT [ BY ] increment ]
           [ MINVALUE minvalue | NO MINVALUE ] [ MAXVALUE maxvalue | NO MAXVALUE ]
           [ START [ WITH ] start ] [ CACHE cache ] [ [ NO ] CYCLE ]
           [ OWNED BY { table.column | NONE } ]


       CREATE  SEQUENCE creates a new sequence number generator. This involves
       creating and initializing a new special single-row table with the  name
       name. The generator will be owned by the user issuing the command.

       If a schema name is given then the sequence is created in the specified
       schema. Otherwise it is  created  in  the  current  schema.   Temporary
       sequences  exist  in a special schema, so a schema name cannot be given
       when creating a temporary sequence.  The sequence name must be distinct
       from  the name of any other sequence, table, index, or view in the same

       After a sequence is created, you use the  functions  nextval,  currval,
       and  setval  to operate on the sequence. These functions are documented
       in in the documentation.

       Although you cannot update a sequence directly, you  can  use  a  query

       SELECT * FROM name;

       to  examine  the  parameters  and  current  state  of  a  sequence.  In
       particular, the last_value field of the sequence shows the  last  value
       allocated  by  any session. (Of course, this value might be obsolete by
       the time it’s printed, if other sessions  are  actively  doing  nextval


              If  specified,  the  sequence  object  is  created only for this
              session, and is automatically dropped on session exit.  Existing
              permanent  sequences with the same name are not visible (in this
              session) while the temporary sequence exists,  unless  they  are
              referenced with schema-qualified names.

       name   The  name  (optionally  schema-qualified)  of the sequence to be

              The optional clause INCREMENT BY increment specifies which value
              is  added to the current sequence value to create a new value. A
              positive value will make an ascending sequence, a negative one a
              descending sequence. The default value is 1.


              The  optional  clause  MINVALUE  minvalue determines the minimum
              value a sequence can generate. If this clause is not supplied or
              NO  MINVALUE  is  specified,  then  defaults  will  be used. The
              defaults  are  1  and  -263-1  for  ascending   and   descending
              sequences, respectively.


              The  optional  clause  MAXVALUE  maxvalue determines the maximum
              value for the sequence. If this clause is  not  supplied  or  NO
              MAXVALUE  is  specified,  then  default values will be used. The
              defaults  are  263-1  and  -1  for  ascending   and   descending
              sequences, respectively.

       start  The  optional  clause  START  WITH start  allows the sequence to
              begin anywhere. The  default  starting  value  is  minvalue  for
              ascending sequences and maxvalue for descending ones.

       cache  The  optional  clause  CACHE  cache  specifies how many sequence
              numbers are 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), and this is also the default.


       NO CYCLE
              The CYCLE option allows 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,

              If NO CYCLE  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,  NO  CYCLE  is  the

       OWNED BY table.column

              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. The specified table must have the same owner and be in the
              same  schema  as  the  sequence.   OWNED  BY  NONE, the default,
              specifies that there is no such association.


       Use DROP SEQUENCE to remove a sequence.

       Sequences are based on bigint arithmetic, so the  range  cannot  exceed
       the   range   of   an   eight-byte   integer  (-9223372036854775808  to
       9223372036854775807). On  some  older  platforms,  there  might  be  no
       compiler  support  for eight-byte integers, in which case sequences use
       regular integer arithmetic (range -2147483648 to +2147483647).

       Unexpected results might be obtained if a cache  setting  greater  than
       one  is  used  for  a sequence object that will be used concurrently by
       multiple sessions. Each session  will  allocate  and  cache  successive
       sequence  values  during one access to the sequence object and increase
       the sequence object’s last_value accordingly.  Then, the  next  cache-1
       uses  of  nextval  within  that  session simply return the preallocated
       values without touching the sequence object. So, any numbers  allocated
       but  not  used  within  a  session will be lost when that session ends,
       resulting in ‘‘holes’’ in the sequence.

       Furthermore, although multiple  sessions  are  guaranteed  to  allocate
       distinct sequence values, the values might be generated out of sequence
       when all the sessions are considered. For example, with a cache setting
       of  10, session A might reserve values 1..10 and return nextval=1, then
       session B might reserve values  11..20  and  return  nextval=11  before
       session A has generated nextval=2. Thus, with a cache setting of one it
       is safe to assume that nextval values are generated sequentially;  with
       a  cache  setting  greater  than  one  you  should only assume that the
       nextval values are all distinct, not that  they  are  generated  purely
       sequentially.  Also,  last_value will reflect the latest value reserved
       by any session, whether or not it has yet been returned by nextval.

       Another consideration is that a setval executed on such a sequence will
       not  be  noticed  by  other  sessions  until  they  have  used  up  any
       preallocated values they have cached.


       Create an ascending sequence called serial, starting at 101:

       CREATE SEQUENCE serial START 101;

       Select the next number from this sequence:

       SELECT nextval(’serial’);


       Select the next number from this sequence:

       SELECT nextval(’serial’);


       Use this sequence in an INSERT command:

       INSERT INTO distributors VALUES (nextval(’serial’), ’nothing’);

       Update the sequence value after a COPY FROM:

       COPY distributors FROM ’input_file’;
       SELECT setval(’serial’, max(id)) FROM distributors;


       CREATE SEQUENCE conforms  to  the  SQL  standard,  with  the  following

       · The standard’s AS <data type> expression is not supported.

       · Obtaining the next value is done using the nextval() function instead
         of the standard’s NEXT VALUE FOR expression.

       · The OWNED BY clause is a PostgreSQL extension.


       ALTER SEQUENCE [alter_sequence(7)], DROP SEQUENCE [drop_sequence(7)]