CREATE SEQUENCE — define a new sequence generator
CREATE [ TEMPORARY | TEMP ] SEQUENCE [ IF NOT EXISTS ]name[ ASdata_type] [ INCREMENT [ BY ]increment] [ MINVALUEminvalue| NO MINVALUE ] [ MAXVALUEmaxvalue| NO MAXVALUE ] [ START [ WITH ]start] [ CACHEcache] [ [ NO ] CYCLE ] [ OWNED BY {table_name.column_name| 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, view, or foreign table 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
   Section 9.16.
  
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.)
  
TEMPORARY or TEMPIf 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.
IF NOT EXISTSDo not throw an error if a relation with the same name already exists. A notice is issued in this case. Note that there is no guarantee that the existing relation is anything like the sequence that would have been created - it might not even be a sequence.
nameThe name (optionally schema-qualified) of the sequence to be created.
data_type      The optional
      clause AS 
      specifies the data type of the sequence.  Valid types are
      data_typesmallint, integer,
      and bigint.  bigint is the
      default.  The data type determines the default minimum and maximum
      values of the sequence.
     
increment      The optional clause INCREMENT BY  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.
     increment
minvalueNO MINVALUE      The optional clause MINVALUE  determines
      the minimum value a sequence can generate. If this clause is not
      supplied or minvalueNO MINVALUE is specified, then
      defaults will be used.  The default for an ascending sequence is 1.  The
      default for a descending sequence is the minimum value of the data type.
     
maxvalueNO MAXVALUE      The optional clause MAXVALUE  determines
      the maximum value for the sequence. If this clause is not
      supplied or maxvalueNO MAXVALUE is specified, then
      default values will be used.  The default for an ascending sequence is
      the maximum value of the data type.  The default for a descending
      sequence is -1.
     
start      The optional clause START WITH  allows the
      sequence to begin anywhere.  The default starting value is
      start minvalue for
      ascending sequences and maxvalue for descending ones.
     
cache      The optional clause 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.
     cache
CYCLENO 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_name.column_nameOWNED 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.
     
   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).
  
   Because nextval and setval calls are never
   rolled back, sequence objects cannot be used if “gapless”
   assignment of sequence numbers is needed.  It is possible to build
   gapless assignment by using exclusive locking of a table containing a
   counter; but this solution is much more expensive than sequence
   objects, especially if many transactions need sequence numbers
   concurrently.
  
   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');
 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;   CREATE SEQUENCE conforms to the SQL
   standard, with the following exceptions:
   
      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.