Question

My database structure is as follows:

I have scheduletimes which have a classtime. Each scheduletime has a tclass associated with it that has a duration. I would normally use a join of some sort to grab the duration, however, since I am using the overlaps comparison in postgres I am not sure if this is possible. The query would look something like this…

Select (scheduletimes.classtime, scheduletimes.classtime + interval 
(select duration from tclasses where tclass.id = scheduletimes.tclass_id) minutes) OVERLAPS 
(06:50:00, 07:20:00) from schedules where
day = 1 and
schedule_id = 14;

Answer 1

You can use a subquery, but in your example you are mixing the literal format with a value from a column, which won’t work. And generally it is better to JOIN rather than to use a subquery, so you might want something like this:

SELECT
    scheduletimes.*,
    (scheduletimes.classtime, scheduletimes.classtime
         + (interval '1 minute' * tclasses.duration))
       OVERLAPS (time '06:50:00', time '07:20:00')
  FROM scheduletimes
  JOIN tclasses ON tclasses.id = scheduletimes.tclass_id
  WHERE day = 1
    AND schedule_id = 14;