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

基本上，我想按照它們覆蓋的目標肌肉的數量來排序練習（在示例中，目標肌肉是 4 和 11）。 但是，子查詢（出於某種原因？）不知道 e 是什么，所以它不起作用。

關於如何獲取此查詢以正確排序我的結果的任何想法？ 謝謝！

編輯：在蘭迪的有用評論之后想出了這個。

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

非常感謝！

Answer 1

MySQL 中的 SQL 子查詢具有類似於“本地命名空間”的內容。 我沒有能力測試，但你可能正在尋找這樣的東西：

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`

但是，在某些情況下，您根本不必使用子查詢。

Answer 2

了解表格的結構可能會有所幫助。 我建議類似的解決方案。

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

如果我理解正確，您根本不需要子查詢

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