CREATE SEQUENCE(7)                                        SQL Commands                                        CREATE SEQUENCE(7)



NAME
       CREATE SEQUENCE - define a new sequence generator


SYNOPSIS
       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 } ]


DESCRIPTION
       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
       schema.

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

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

       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 calls.)

PARAMETERS
       TEMPORARY or TEMP
              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 created.

       increment
              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.

       minvalue

       NO MINVALUE
              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.

       maxvalue

       NO MAXVALUE
              The optional clause MAXVALUE maxvalue determines the maximum value for the sequence. If this clause  is  not  sup-
              plied  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  min-
              value 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.

       CYCLE

       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, respectively.

              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 default.

       OWNED BY table.column

       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. 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.

NOTES
       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 gener-
       ated 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 ses-
       sion 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.

EXAMPLES
       Create an ascending sequence called serial, starting at 101:

       CREATE SEQUENCE serial START 101;


       Select the next number from this sequence:

       SELECT nextval('serial');

        nextval
       ---------
            101


       Select the next number from this sequence:

       SELECT nextval('serial');

        nextval
       ---------
            102


       Use this sequence in an INSERT command:

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


       Update the sequence value after a COPY FROM:

       BEGIN;
       COPY distributors FROM 'input_file';
       SELECT setval('serial', max(id)) FROM distributors;
       END;


COMPATIBILITY
       CREATE SEQUENCE conforms to the SQL standard, with the following exceptions:

       o The standard's AS <data type> expression is not supported.

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

       o The OWNED BY clause is a PostgreSQL extension.

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



SQL - Language Statements                                  2011-09-22                                         CREATE SEQUENCE(7)