Question

我正在尝试获取两个表的计数值并使用成员id作为键来计算其他表的行数，到目前为止我有这个代码，但它为comCount输出一个大值，为chatCount输出空值。这是我的代码

SELECT members.*
, comments.commenter_id
, cb.user_id
, COUNT(comments.comment) AS comCount
, COUNT(cb.message) AS chatCount
FROM members 
INNER JOIN comments ON members.id = comments.commenter_id
INNER JOIN chat_box AS cb ON members.id = cb.user_id
WHERE members.id ='$profileId'`

Answer 1

SELECT  members.* , 
        a.commenter_id , 
        b.user_id , 
        a.totalComment , 
        b.totalChat
FROM    members 
        INNER JOIN 
        (
            SELECT commenter_id, COUNT(*) totalComment
            FROM comments
            GROUP BY commenter_id
        ) a ON members.id = a.commenter_id
        INNER JOIN 
        (
            SELECT user_id, COUNT(*) totalChat
            FROM chat_box 
            GROUP BY user_id            
        ) b  ON members.id = b.user_id
WHERE   members.id = '$profileId'

作为旁注，如果值（ s ）来自外部，则查询容易被SQL Injection攻击。请查看下面的文章，了解如何防止它。通过使用PreparedStatements，您可以摆脱在值周围使用单引号。

How to prevent SQL injection in PHP?

Answer 2

SELECT members.*
, comments.commenter_id
, cb.user_id
,(select  COUNT(1) from comments where commenter_id = members.id) AS comCount
,(select count(1) from chat_box where user_id = members.id) AS chatCount
FROM members 
WHERE members.id ='$profileId'`

加入三个不同的表

2 个答案: