Question

我有两张桌子：“会员”和“问题”。每个成员都可以提出多个问题。

我想检索被问过3个以上问题的成员数

到目前为止我的查询：

SELECT DISTINCT  q.question_id, COUNT( q.question_id ) AS question_id_count
FROM member m

inner join question q on m.member_id = q.member_id

GROUP BY m.member_id
HAVING (
COUNT( q.question_id ) >3
)

如何改善此查询？谢谢

Answer 1

这是不正确的。

如果您按成员进行分组，则应显示成员！

distinct是不必要的，每个成员只会显示一次（除非你有重复的成员！）

考虑此评论：

您想要检索要求超过3的成员数量吗？问题或每个成员要求更多问题的问题超过3个问题？

第一个选项是

select count(*) from 
(SELECT m.member_id 
    FROM member m
    inner join question q on m.member_id = q.member_id
    GROUP BY m.member_id
    HAVING COUNT(q.question_id) >3) T

第二个选项是

SELECT m.member_id, COUNT( q.question_id ) AS question_id_count
FROM member m
inner join question q on m.member_id = q.member_id
GROUP BY m.member_id
HAVING COUNT(q.question_id) >3

Answer 2

根据您的声明i want to retrieve count of member whose asked more than 3 question ，加入表格并按memberID分组。

SELECT  a.member_id, count(b.member_id) totalQuestion
FROM    member a
        INNER JOIN question b
            ON a.member_id = b.member_id
GROUP BY a.member_id
HAVING count(b.member_id) > 3

正如您在此条件{$ 1}}上看到的那样，它通过ON a.member_id = b.member_id链接两个表格（您可以自由地将columnName更改为您桌面上存在的名称。）

MySQL计数一对多关系的查询

2 个答案: