Question

I’m creating a room suggestion feature for a room reservation system and I’m trying to figure out how to attack this query. So far I’ve got it excluding what rooms are reserved and in conflict with the desired room. Here is my query:

"SELECT * FROM room 
 WHERE roomcode NOT IN 
      (SELECT room FROM event 
       INNER JOIN room ON event.room = room.roomcode 
       WHERE ( 
                 (begintime <= $start AND endtime >= end) 
              OR (begintime >= $start AND endtime <= $end)
              OR (begintime <= $start AND endtime <= $end AND endtime >= $start) 
              OR (begintime >= $start AND endtime >= $end AND begintime <= $end) 
             ) 
             AND room = '$room' 
             OR room IN ($rooms) 
       ) 
       AND capacity >= $capacity AND min_capacity <= $capacity";

I’m sorry if that’s a mess.

The information I’m unable to get to right now is a list of rooms that become inactive when a particular room is reserved. For example, a room (n103abc) has three partitions. The whole room can be reserved as one, causing the three parts and their other combinations (n103a, n103b, n103c, n103ab, n103bc) to become inactive. Each room has a column in the database with the rooms it sets inactive formatted as a list separated only by a comma, no spaces.

Basically what’s going on is I’m trying to select rooms that don’t fall in any of the begintime/endtime conditions, aren’t the room reserved in those that fall into the begintime/endtime conditions, and aren’t inactive.

Any suggestions? I know that was a pain in the butt, but I hope someone can show me the light here. I’ve been staring at this for the last 5 hours with no progress. Thanks.

Answer 1

The sentence…

“Each room has a column in the database with the rooms it sets inactive formatted as a list separated only by a comma, no spaces.”

…means your table is not even in the first normal form.

So, you’d probably want to model this hierarchy in a more relational way – for example by introducing a room.parent_roomcode field that is a FOREIGN KEY toward the room.roomcode. If the parent_roomcode is NULL, this is the “parent” and if it’s non-NULL then this is the “child” (i.e. becomes inactive when parent becomes reserved). Let’s also assume this hierarchy is single-level only (i.e. there are no “grandchildren”).

You could then query (roughly) like this:

SELECT *
FROM room
WHERE
    NOT EXISTS (
        SELECT *
        FROM events
        WHERE
            NOT ($end <= begintime OR endtime <= $start)
            AND (
                events.room = room.roomcode
                OR events.room = room.parent_roomcode
            )
    )
    AND min_capacity <= $capacity
    AND $capacity <= capacity

In plain English, select rooms such that:

• There is no event such that:
  • It intersects with given time interval,
  • and is associated with the room or its parent.
• And the capacity is appropriate.

Details:

• $end <= begintime OR endtime <= $start means the event is completely before or completely after the given interval (this works under assumption that $start <= $end and begintime <= endtime). Applying NOT gives an event that is either partially or completely in the interval.
• events.room = room.parent_roomcode gives events that are connected to parent, meaning the child room is inactive. Since we are dealing with a single-level hierarchy, there is no need for a recursive query.