Question

我有两个表来存储来自两个不同用户的评论

Table1

id_table1 | comment | id_user | id_post

Table2

id_table2 | comment | id_someOtherUser | id_post

我真的只想在这两个中只有一个表，因为评论发布在同一个帖子上，但我不能，因为我有两个不同类型的用户的两个不同的ID。

我的问题是如何根据两个表格中的评论数量列出所有帖子DESC？

如果我做的话

SELECT P.*, count(*) as count from Table1 AS T1
LEFT JOIN post AS P ON T1.id_post = P.id_post GROUP BY P.id_post ORDER BY count DESC

然后我有table1的帖子，同样可以为table2完成，但是如何将两个表中的注释组合在一起呢？

Answer 1

我会使用UNION ALL以通用格式合并两个评论表，然后执行JOIN：

SELECT P.*, TC.count
FROM (
    SELECT Ts.id_post, count(*) AS count
    FROM (
          SELECT id_post FROM Table1
          UNION ALL
          SELECT id_post FROM Table2
    ) AS Ts
    GROUP BY Ts.id_post
) AS TC
LEFT JOIN post AS P ON TC.id_post = P.id_post
GROUP BY P.id_post
ORDER BY TC.count DESC

Answer 2

解决此问题的一种方法是对每个表执行单独的计数，然后执行完整的外部联接，并获取每个计数的总和：

SELECT id_post, (count1 + count2) AS total_count FROM (SELECT id_post, count(*) as count1 from Table1 AS T1 FULL OUTER JOIN (SELECT id_post, count(*) as count2 from Table2 AS T2) USING(id_post)) ORDER BY total_count DESC

将mysql count（*）组合为两个不同的表，同一列

2 个答案: