Firebird - Converting stored integer to time equivalent

I am currently working on a Firebird database which stores slots for a time (like appointments). In the data the timeslot is stored in an Integer format but is not the slot time.

Example: Slot Time: 11am Database Value: 660

The database value is represented as the number of minutes since midnight. So 11am is 660 minutes from midnight. Or 12noon is 720

Question How, in Firebird, can a convert this 660 to display as 1100 (still an integer) or 540 as 900 (basically 9am)?

Solution

What you have stored into database is minutes since start of the day. So you just divide with 60 to get hours. Keep in mind that in SQL if both arguments of the division are integers you'll get integer as an answer, not decimal! Something like following should work for you (assuming the number of minutes is stored to timeslot field):

SELECT 
 cast(timeslot / 60 as varchar(2)) || 
   case
     when mod(timeslot, 60) < 10 then '0'|| mod(timeslot, 60)
     else mod(timeslot, 60)
   end
FROM t

This should give you 1130 for 11:30 am, not 1150 (11,5 hours).

Also see the DATEADD function.