MySQL: ORDER BY A COUNT of rows from another table?

Question

SELECT e.*,
(
    SELECT COUNT(*) FROM
    (
        SELECT tm.exerciseID FROM exercise_targetedmuscles tm
        WHERE tm.exerciseID = e.exerciseID
        AND tm.isPrimary = 1
        AND tm.targetedMuscleID IN (4,11)
    ) as musclesCovered
) as numMusclesCovered
FROM exercises e
ORDER BY numMusclesCovered DESC

Basically, I want to order the exercises by the number of targetted muscles they cover (in the example, the targetted muscles are 4 and 11). However, the subquery (for some reason?) doesn't know what e is, so it does not work.

Any ideas as to how I can get this query to order my results properly? Thanks!

EDIT: came up with this after Randy's helpful comment.

SELECT COUNT(tm.targetedMuscleID) as numMusclesCovered, e.*, tm.* FROM exercise_targetedmuscles tm

JOIN exercises e ON tm.exerciseID = e.exerciseID

WHERE tm.isPrimary = 1
AND tm.targetedMuscleID IN (4,11)

GROUP BY tm.exerciseID

ORDER BY numMusclesCovered DESC

thanks so much!

Answer 1

SQL subqueries in MySQL has something like "local namespace". I haven`t got ability to test, but you may be searching for something like this:

SELECT `data`.* FROM (
   SELECT COUNT(tm.targetedMuscleID) as `count`,tm.targetedMuscleID FROM exercise_targetedmuscles tm
   LEFT JOIN `exercises` as `e` ON (`tm`.`exerciseID`=`e`.`exerciseID`)
   WHERE
       tm.isPrimary = 1
   AND
       tm.targetedMuscleID IN (4,11)
   GROUP BY tm.targetedMuscleID
) as `data`
ORDER BY `data`.`count`

But, in some cases, you do not have to use subquery at all.

Answer 2

Knowing how the tables are structured might be helpful. I suggest a solution similar to this.

SELECT e.*, tm.*, COUNT(tm.targetedMuscleID) AS coveredMuscles
FROM exercises AS e
JOIN exercise_targetedmuscles AS tm ON tm.exerciseID = e.exerciseID
WHERE tm.isPrimary = 1 AND tm.targetedMuscleID IN (4, 11)
GROUP BY e.exerciseID
ORDER BY coveredMuscles;

Answer 3

If I understand correctly, you don't need subquery at all

SELECT count(tm.targetedMuscleID) as num_muscles, e.exerciseID 
FROM exercise_targetedmuscles tm, exercises e
WHERE tm.exerciseID = e.exerciseID
AND tm.isPrimary = 1
AND tm.targetedMuscleID IN (4,11)
GROUP BY e.exerciseID
order by num_muscles