LeetCode（数据库）- 每个帖子的评论数

Posted 2021-09-11 程序员牧码

题目链接：点击打开链接

题目大意：略。

解题思路：略。

AC 代码

-- 解决方案(1)
SELECT t1.sub_id post_id, COUNT(t2.parent_id) number_of_comments
FROM (SELECT * FROM Submissions WHERE parent_id IS NULL GROUP BY sub_id) t1
LEFT JOIN 
(SELECT * FROM Submissions WHERE parent_id IS NOT NULL GROUP BY sub_id, parent_id) t2
ON t1.sub_id = t2.parent_id
GROUP BY post_id
ORDER BY post_id

-- 解决方案(2)
SELECT post_id, COUNT(sub_id) AS number_of_comments
FROM (
    SELECT DISTINCT post.sub_id AS post_id, sub.sub_id AS sub_id
    FROM Submissions post
    LEFT JOIN Submissions sub
    ON post.sub_id = sub.parent_id
    WHERE post.parent_id is null
) T
GROUP BY post_id
ORDER BY post_id ASC