SERIAL is a number generator that generates positive integers starting with 1 or a specified value.
SERIAL can be used as a
DEFAULT specification for columns (DEFAULT SERIAL) that can only contain fixed point numbers. The maximum value generated is (10**n)-1 if DEFAULT SERIAL is defined for a column of the data type FIXED (n).SERIAL columns can only be assigned a value when a row is inserted. The values of a SERIAL column cannot be changed with an UPDATE statement. A SERIAL column, therefore, can be used to determine the insertion sequence and identify a row in a table uniquely.