TIME_ADD(time_expression, INTERVAL int64_expression part) adds int64_expression units of part to the time object. For example, the outcome of:
TIME_ADD(TIME '15:30:00', INTERVAL 5 MINUTE) is 15:35:00.
TIME_DIFF(time_expression_a, time_expression_b, part) finds the whole number of part between time_expression_a and time_expression_b . If time_expression_a is earlier than time_expression_b, the outcome is negative. For example, the outcome of:
TIME_DIFF(TIME '15:30:00', TIME '15:40:00', MINUTE) is -10.