596. Classes With at Least 5 Students : leetcode

WITH cnt AS   (select      DISTINCT class,
                COUNT(student) OVER(PARTITION BY class) as student_cnt
                FROM        Courses)


SELECT  class
FROM    cnt
WHERE   student_cnt >= 5

이렇게 풀면 쿼리 처리 시간이 오래 걸린다.

select class 
from courses
group by class
having count(class) >= 5

이러면 줄어들고

select class 
from courses
group by class
having count(class)>4

이러면 더 줄어든다.