A constant holds a value that does not change. A constant declaration specifies the name, data type, and value of the constant and allocates storage for it. The declaration can also impose the
Name of the constant that you are declaring.
Data type for which a variable can be declared with an initial value.
NULL constraint on the constant. For information about this constraint, see "NOT NULL Constraint".
Initial value for the constant. expression must have a data type that is compatible with datatype. When constant_declaration is elaborated, the value of expression is assigned to constant.