Sequences in SQL are used to create the auto generated values which are normally integers that follows a sequence.

CREATE SEQUENCE [schema.]sequence_name
  [ AS datatype ]
  [ START WITH value ]
  [ INCREMENT BY value ]
  [ MINVALUE value | NO MINVALUE ]
  [ MAXVALUE value | NO MAXVALUE ]
  [ CYCLE | NO CYCLE ]
  [ CACHE value | NO CACHE ];

AS datatype : It can be BIGINT, INT, TINYINT, SMALLINT, DECIMAL, or NUMERIC. If datatype is not specified, the sequence will default to a BIGINT datatype.

START WITH value : The starting value that the sequence returns intially.

INCREMENT BY value : It can be either a positive or negative value. If a positive value is specified, the sequence will be an ascending sequence of values. If a negative value is specified, the sequence will be a descending sequence of values.

MINVALUE value : The minimum value for the sequence

NO MINVALUE: It means that  no minimum value is there for the sequence .

MAXVALUE value : The maximum value given for the sequence.

NO MAXVALUE : It means that there is no maximum value specified for the sequence.

CYCLE : It means that the sequence will start over once it has completed the sequence.

NO CYCLE : When sequence gets completed it will raise an error after that.

CACHE value : It caches the sequence numbers to minimize disk IO.

NO CACHE : It does not cache the sequence numbers.

CREATE SEQUENCE contacts_seq
  AS BIGINT
  START WITH 1
  INCREMENT BY 1
  MINVALUE 1
  MAXVALUE 99999
  NO CYCLE
  CACHE 10;