LeetCode 2356. Number of Unique Subjects Taught by Each Teacher / MySQL / Easy (From절 서브쿼리)

📚문제

출처 : LeetCode(https://leetcode.com/problems/number-of-unique-subjects-taught-by-each-teacher/)

📝풀이

# Write your MySQL query statement below
SELECT teacher_id
     , COUNT(subject_id) AS cnt
FROM (SELECT teacher_id,subject_id,COUNT(*)
FROM Teacher
GROUP BY teacher_id,subject_id) AS teacher_grouping
GROUP BY teacher_id

FROM 절 서브쿼리를 활용하여 풀이