Question

Is there any better way to make this query work? I’m looking for a more efficient solution, if there is one available.

SELECT `unitid`, `name` FROM apartmentunits WHERE aptid IN (
    SELECT `aptid` FROM rentconditionsmap WHERE rentcondid = 4 AND condnum = 1
) AND aptid IN (
    SELECT `aptid` FROM rentconditionsmap WHERE rentcondid = 2 AND condnum = 1
) ORDER BY name ASC 

Answer 1

I think you want a self-join here. Join table rentconditionsmap to itself, and indicate the conditions on either side of the join. Then join the results of that query into apartmentunits.

(Note: haven’t tested this, may require some tweaking…)

SELECT `unitid`, `name` FROM `apartmentunits` 
 WHERE `unitid` IN (
        SELECT `unitid` FROM `rentconditionsmap` r1, `rentconditionsmap` r2
         WHERE r1.`unitid` = r2.`unitid`
           AND r1.`rentcondid` = 4
           AND r1.`condnum` = 1
           AND r2.`rentcondid` = 2
           AND r2.`condnum` = 1)
 ORDER BY `name` ASC