SQL clock classes

SQL clock classes are intended to provide a common context for transferring data between applications. Standard business computing practices distinguish these time measurement contexts:

• Dates, used for appointments and generally accurate to the second, at most.
• Time, the standard to which one might set an alarm clock. Time is generally relative to midnight.
• Timestamps, or extremely accurate dates. For example, a timestamp might be used to monitor the microsecond-level fluid flow rate in an oil pipeline.

TSQLDate is a concrete class based on a reference date of March 1, 2000. Time is measured in seconds from the reference date. Dates earlier than the reference date are negative. Later dates are positive. Use instances of TSQLDate with appointments, calendars, or in any other client context that demands a time based on the reference date.

TSQLTime is a concrete class based on a reference time of midnight. Time is measured in seconds from the reference time. Use instances of TSQLTime for alarms, or in any other client context that demands a time based on the reference time.

TSQLTimestamp is a concrete class that extends TSQLDate by adding accuracy to the picosecond. Use instances of this class in contexts demanding extremely accurate time measurements.