Timestamps can be subtracted, incremented, or decremented.
The result of subtracting one timestamp (TS2) from another (TS1) is a timestamp duration that specifies the number of years, months, days, hours, minutes, seconds, and microseconds between the two timestamps. The data type of the result is DECIMAL(20,6). If TS1 is greater than or equal to TS2, TS2 is subtracted from TS1. If TS1 is less than TS2, however, TS1 is subtracted from TS2 and the sign of the result is made negative. The following procedural description clarifies the steps involved in the operation RESULT = TS1 - TS2.
If MICROSECOND(TS2) <= MICROSECOND(TS1)
then MICROSECOND(RESULT) = MICROSECOND(TS1) -
MICROSECOND(TS2).
If MICROSECOND(TS2) >MICROSECOND(TS1)
then MICROSECOND(RESULT) = 1000000 +
MICROSECOND(TS1) - MICROSECOND(TS2)
and SECOND(TS2) is incremented by 1.
The seconds and minutes part of the timestamps are subtracted as specified
in the rules for subtracting times.
If HOUR(TS2) <= HOUR(TS1)
then HOUR(RESULT) = HOUR(TS1) - HOUR(TS2).
If HOUR(TS2) > HOUR(TS1)
then HOUR(RESULT) = 24 + HOUR(TS1) - HOUR(TS2)
and DAY(TS2) is incremented by 1.
The date part of the timestamps is subtracted as specified
in the rules for subtracting dates.
The result of adding a duration to a timestamp, or of subtracting a duration from a timestamp, is itself a timestamp. Date and time arithmetic is performed as previously defined, except that an overflow or underflow of hours is carried into the date part of the result, which must be within the range of valid dates. Microseconds overflow into seconds.