Question

I have a table structure like:

 Events (id, name, start, end, venue)
 Venues (id, name)

Where Events.start and end are representing start and end datetimes for the event. Events.veuue is a foreign key to Venues. I want to select all available venues in a time range. What might the SQL look like. At the moment, I have difficulties figuring that out…

Answer 1

You’ll need a NOT EXISTS to get rows from Events that don’t overlap your time ranges. I think this should do the job:

SELECT v.id, v.name
FROM 
  Venues v 
WHERE NOT EXISTS (
  SELECT venue FROM Events e
  WHERE [searchdate] BETWEEN start AND end
   AND v.id = e.venue
)

The above uses a single datetime [searchdate]. If you need a start/end range of dates to check venues for, use a WHERE clause like:

WHERE 
  [searchstartdate] BETWEEN start AND end 
  OR [searchenddate]  BETWEEN start AND end 

So, if either [searchstartdate] or [searchenddate] overlaps the event, a row will match.