ADDTIME/SUBTIME(t,a) 

ADDTIME(t,a) and SUBTIME(t,a) are time functions that calculate a time/timestamp value in the past or future.

Value t: When used in a function, the expression t (time_or_timestamp_expression) must supply a time value, a time stamp value, or an alphanumeric value that matches the current time or time stamp format.

Value a: When used in a function, the expression a (time_expression) must supply a time value or an alphanumeric value that matches the current time format.

	Result of the Function ADDTIME(t,a)/SUBTIME(t,a)
Addition of a to t/ Subtraction of a from t	Time or time stamp value
SUBTIME(t,a) and t and a are time values	a must be less than t, otherwise an error is output
t or a is NULL value	NULL value