DBMS compliance with SQL-92 intervals is spotty, so this section is meant to be used as a reference. DBMSes have their own extended data types and functions that calculate intervals and perform date and time arithmetic.
Use interval data types to represent intervals between dates and times of day. An interval value has these characteristics:
It stores the quantity of time between two datetime values. Between 09:00 and 13:30 is an interval of 04:30 (4 hours and 30 minutes), for example. If you subtract two datetime values, you get an interval.
It can be used to increment or decrement a datetime value; see “"Performing Date and Time ...