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

NAME

       CREATE SEQUENCE - define a new sequence generator

SYNOPSIS

       CREATE [ TEMPORARY | TEMP ] SEQUENCE seqname [ INCREMENT increment ]
	   [ MINVALUE minvalue ] [ MAXVALUE maxvalue ]
	   [ START start ] [ CACHE cache ] [ CYCLE ]

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

       seqname
	      The name (optionally schema-qualified) of a sequence to be created.

       increment
	      The  INCREMENT increment clause is optional. A positive value will make an ascending sequence, a negative one a descending sequence.
	      The default value is one (1).

       minvalue
	      The optional clause MINVALUE minvalue determines the minimum value a sequence can generate. The  defaults  are  1  and  -2^63-1  for
	      ascending and descending sequences, respectively.

       maxvalue
	      The  optional  clause  MAXVALUE maxvalue determines the maximum value for the sequence. The defaults are 2^63-1 and -1 for ascending
	      and descending sequences, respectively.

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

       cache  The  CACHE  cache  option 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) and this is also the default.

       CYCLE  The optional CYCLE keyword 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.  Without CYCLE, after the limit is reached nextval calls will return an error.

   OUTPUTS
       CREATE SEQUENCE
	      Message returned if the command is successful.

       ERROR: Relation 'seqname' already exists
	      If the sequence specified already exists.

       ERROR: DefineSequence: MINVALUE (start) can't be >= MAXVALUE (max)
	      If the specified starting value is out of range.

       ERROR: DefineSequence: START value (start) can't be < MINVALUE (min)
	      If the specified starting value is out of range.

       ERROR: DefineSequence: MINVALUE (min) can't be >= MAXVALUE (max)
	      If the minimum and maximum values are inconsistent.

DESCRIPTION

       CREATE SEQUENCE will enter a new sequence number generator into the current database. This involves creating and initializing a new single-
       row table with the name seqname.  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 (the one at
       the front of the search path; see CURRENT_SCHEMA()).  TEMP sequences exist in a special schema, so a schema name may not be given when cre-
       ating a TEMP 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 functions are documented
       in the User's Guide.

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

       SELECT * FROM seqname;

       to examine the parameters and current state of a sequence. In particular, the last_value field of the sequence shows the last  value  allo-
       cated  by  any  backend	process.  (Of  course,	this value may be obsolete by the time it's printed, if other processes are actively doing
       nextval calls.)

	      Caution: Unexpected results may be obtained if a cache setting greater than one is used for a sequence object that will be used con-
	      currently  by  multiple  backends. Each backend 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 backend  simply
	      return  the  preallocated values without touching the shared object. So, any numbers allocated but not used within a session will be
	      lost when that session ends. Furthermore, although multiple backends are guaranteed to allocate distinct sequence values, the values
	      may  be  generated  out  of sequence when all the backends are considered. (For example, with a cache setting of 10, backend A might
	      reserve values 1..10 and return nextval=1, then backend B might reserve values 11..20 and return nextval=11  before  backend  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 backend, 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 backends until	they  have
	      used up any preallocated values they have cached.

   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 may be no compiler support for eight-byte integers, in which case sequences use  regu-
       lar integer arithmetic (range -2147483648 to +2147483647).

       When cache is greater than one, each backend uses its own cache to store preallocated numbers.  Numbers that are cached but not used in the
       current session will be lost, resulting in ``holes'' in the sequence.

USAGE

       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
       -------
	   114

       Use this sequence in an INSERT:

       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

   SQL92
       CREATE SEQUENCE is a PostgreSQL language extension.  There is no CREATE SEQUENCE statement in SQL92.

SQL - Language Statements					    2002-11-22							CREATE SEQUENCE(7)