获取从表中MySQL查询

Question

前3名评论员我有3个表

comments(id,question_id, user_Id) // here the user_id is of the user who has asked the question 
questions(id,q_desc, user_id) 
users(id, name, rank) 

用户可以提出问题，并就有关问题可以发表评论。

我需要一份报告，其中我想要显示每个问题的最多3个排名最高的用户，他们已对其发表了评论，但是问过该问题的用户不应该在该特定问题的报告中，但他也有权评论他的问题。

编辑:::

Select * from comments inner join users(comments.user_id=u.id) group by question_id order by user.rank desc 

Answer 1

它的混乱，但它的工作原理：

SELECT 
    a.question_id, a.user_id, a.name, a.rank 
FROM 
(
    SELECT a.*, b.name, b.rank 
    FROM 
    (
     SELECT DISTINCT b.question_id, b.user_id 
     FROM questions a 
     INNER JOIN comments b ON a.id = b.question_id AND a.user_id <> b.user_id 
    ) a 
    INNER JOIN users b ON a.user_id = b.id 
) a 
INNER JOIN 
(
    SELECT a.question_id, b.rank 
    FROM 
    (
     SELECT DISTINCT b.question_id, b.user_id 
     FROM questions a 
     INNER JOIN comments b ON a.id = b.question_id AND a.user_id <> b.user_id 
    ) a 
    INNER JOIN users b ON a.user_id = b.id 
) b ON a.question_id = b.question_id AND a.rank <= b.rank 
GROUP BY 
    a.question_id, a.user_id, a.name, a.rank 
HAVING 
    COUNT(1) <= 3 
ORDER BY 
    a.question_id, a.rank DESC 

编辑：这将产生相同的结果，更简洁：

SELECT a.* 
FROM 
(
    SELECT DISTINCT a.question_id, a.user_id, b.name, b.rank 
    FROM comments a 
    INNER JOIN users b ON a.user_id = b.id 
) a 
INNER JOIN 
    questions b ON a.question_id = b.id AND a.user_id <> b.user_id 
INNER JOIN 
(
    SELECT DISTINCT a.question_id, a.user_id, b.rank 
    FROM comments a 
    INNER JOIN users b ON a.user_id = b.id 
) c ON b.id = c.question_id AND a.rank <= c.rank 
GROUP BY 
    a.question_id, a.user_id, a.name, a.rank 
HAVING 
    COUNT(1) <= 3 
ORDER BY 
    a.question_id, a.rank DESC; 

这些解决方案还可以解决已发布mor的用户而不是同一问题中的一条评论。

在SQLFiddle