Home Man
Today's Posts

Linux & Unix Commands - Search Man Pages

RedHat 9 (Linux i386) - man page for create_sequence (redhat section 7)

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

       CREATE SEQUENCE - define a new sequence generator

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

	      If specified, the sequence object is created only for this session, and is automat-
	      ically 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.

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

	      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).

	      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,

	      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,

       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 min-
	      value or maxvalue, respectively.	Without CYCLE, after the limit is reached nextval
	      calls will return an error.

	      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.

       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 gen-
       erator 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  CUR-
       RENT_SCHEMA()).	 TEMP  sequences  exist  in a special schema, so a schema name may not be
       given when creating 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 allocated 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  concurrently  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 preal-
	      located 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.

       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 reg-
       ular integer arithmetic (range -2147483648 to +2147483647).

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

       Create an ascending sequence called serial, starting at 101:

       CREATE SEQUENCE serial START 101;

       Select the next number from this sequence:

       SELECT nextval('serial');


       Use this sequence in an INSERT:

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

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

All times are GMT -4. The time now is 04:08 PM.

Unix & Linux Forums Content Copyrightę1993-2018. All Rights Reserved.
Show Password