SQL查詢優化 - 消除子查詢

Question

我有這個查詢，我想優化它。我使用SELECT和子查詢，並且如果可能的話我只想使用一個SELECT。

有沒有人有任何想法呢？

預先感謝您

SELECT c.* 
FROM course AS c 
JOIN student_course AS sc ON c.id = uc.course_id 
WHERE sc.student_id = '5' AND c.level = (SELECT MAX(level) 
             FROM course 
             JOIN student_course ON c.id = sc.course_id) 
GROUP BY c.category_id 

Answer 1

SELECT c.* 
FROM course AS c 
JOIN student_course AS sc 
ON c.id = sc.course_id 
WHERE sc.student_id = '5' 
GROUP BY c.category_id 
having c.level = MAX(sc.level)