How to SELECT rows from table A that do not match with table B (using time range, based from table B)

Question

Im a student, trying to design a system that can find ALL vacant rooms at a certain time and day, given the schedules of professors based from the existing database of their school. For each rooms, a schedule is generated from 7:30:00 - 19:30:00 (incremental by 00:30:00) to the table named 'room_schedule' . Each schedule of a room is referenced by room_id from another table named 'room_details' . On the other hand, the table 'room_details' is linked to table 'prof_schedule' by room. Schedules of professors are recorded on an existing table 'prof_schedule'.

Here's how the tables look like

TABLE 'room_schedule'

    
    MWF    07:00:00    07:30:00    36
    MWF    07:30:00    08:00:00    36
    MWF    08:00:00    08:30:00    36
    MWF    08:30:00    09:00:00    36
    MWF    09:00:00    09:30:00    36
    MWF    09:30:00    10:00:00    36
    MWF    07:00:00    07:30:00    37
    MWF    07:30:00    08:00:00    37
    MWF    08:00:00    08:30:00    37
    MWF    08:30:00    09:00:00    37
    MWF    09:00:00    09:30:00    37
    MWF    09:30:00    10:00:00    37

    TABLE 'room_details'
           
    36          Biology Room   309   
    37          Physics Room   307


    TABLE 'prof_schedule'
    
    1          Jeffrey Smith   MWF  309     8:00:00     9:30:00     Biology
    2          Ben Williams    MWF  307     8:30:00     10:00:00    Physics

Based from the schedules of professors, i wanted the result for vacant rooms to be like this

RESULT vacant rooms
      
        MWF    07:00:00    07:30:00    Biology Room
        MWF    07:30:00    08:00:00    Biology Room
        MWF    09:30:00    10:00:00    Biology Room
        MWF    07:00:00    07:30:00    Physics Room
        MWF    07:30:00    08:00:00    Physics Room
        MWF    08:00:00    08:30:00    Physics Room

I have tried the query below, but it seems like it removes all records from 'room_schedule' having time_start and time_end from 'prof_schedule'

SELECT day, time_start, time_end,  room_name 
FROM room_details AS rd 
INNER JOIN room_schedule AS rs 
ON rd.room_ID=rs.room_ID 
WHERE (
   (time_start NOT IN(SELECT time_start FROM prof_schedule)) AND 
   (time_end NOT IN (SELECT time_end FROM prof_schedule)) AND 
   (rs.day NOT IN (select day from prof_schedule)) AND 
   (rs.room_id NOT IN (SELECT DISTINCT rd.room_ID from room_details AS rd 
    INNER JOIN prof_schedule AS ps on rd.room=ps.room))
  )

Can someone suggest a query that would show the result I mentioned?

PS The design of the 3rd table (prof_schedule) needs to be retained because they'll be importing these from their existing system to the system I'm designing.

Answer 1

Try something like this and let me know.

SELECT a.day, a.time_start, a.time_end, b.room_name 
FROM `room_schedule` a 
INNER JOIN `room_details` b ON a.room_id = b.room_id
INNER JOIN `prof_schedule` c ON b.room = c.room AND 
IF(a.time_end > c.time_start, a.time_start >= c.time_end, a.time_start < c.time_start)

---

Try using GROUP BY clause like this

SELECT a.*, b.room_name 
FROM `room_schedule` a 
INNER JOIN `room_details` b ON a.room_id = b.room_id
INNER JOIN `prof_schedule` c ON b.room = c.room AND 
IF(a.time_end > c.time_start, a.time_start >= c.time_end, a.time_start < c.time_start)
GROUP BY a.room_id, a.time_start, a.time_end