Constants
A constant (also called a literal) specifies a value. Constants are
classified as 
null constants,
string constants, numeric constants, datetime
constants, or Boolean constants. String constants are further classified as
character, graphic, or binary. Numeric constants are further classified as integer, floating-point,
decimal floating-point, or decimal.
All constants, except null constants, have the attribute NOT NULL. A
negative sign in a numeric constant with a value of zero is ignored.