LeetCode（数据库）- 超过5名学生的课

Posted 2021-05-22 Lux_Sun

题目链接：点击打开链接

 

题目大意：略。

 

解题思路：解决方案(2)，注：COUNT(student) 不能直接在 WHERE 子句中使用，这里将其重命名为 num。

 

AC 代码

-- 解决方案(1)
SELECT rs.class
FROM (SELECT DISTINCT student, class FROM courses) rs
GROUP BY rs.class
HAVING COUNT(1) >= 5

-- 解决方案(2)
SELECT
    class
FROM
    (SELECT
        class, COUNT(DISTINCT student) AS num
    FROM
        courses
    GROUP BY class) AS temp_table
WHERE
    num >= 5;

-- 解决方案(3)
SELECT
    class
FROM
    courses
GROUP BY class
HAVING COUNT(DISTINCT student) >= 5;