Lester wrote:

> If I add date.5 and date.25 I get 6pm in the result

But you shouldn't add two dates (or timestamps), and in Firebird you can't.

What's the sum of 12 October 1948 and 6 July 2007? Or noon plus 4:30 in the morning? Both expressions are meaningless.

You can subtract two dates/timestamps, and that gives you an interval.

And you can add an interval to a date/timestamp (or subtract it), and then you get another date/timestamp.

In Firebird, intervals are
- when subtracting timestamps: numeric(18,9), representing days and fractions of days
- when subtracting dates: integer, representing whole days
- when subtracting time values: numeric(9,4), representing seconds and fractions of seconds

This arithmetic works fine in Firebird SQL, as long as you make sure that you don't confuse date/time values with intervals.

This is allowed:

date/time + interval
date/time - interval
date/time - date/time

This isn't:
date/time + date/time
(with one exception: date + time is allowed, and makes sense)


Paul Vinkenoog