Question

我在MySQL中有3个表

USERS
uid
email
password
created

这是包含所有用户的所有记录的表

PHOTOS
iid
uid
file
thumb
uploaded

这是每个用户发布的所有照片都保存在

上的表格

COMMENTS
cid
iid
uid
message
created

此表是每个用户对每张照片的所有评论都保留在

上的表格

我想要的是一个查询，它会向我回复每个唯一（COUNT）用户的每张照片的评论金额（DISTINCT）。例如（结果输出必须是）：

comment_amount  by_user on_picture
3               1       1
2               2       1
2               1       2
5               2       2
6               2       3

所以输出可以告诉我们它是否格式化（例如）

3 comments posted by USER1 on PICTURE1
2 comments posted by USER2 on PICTURE1

2 comments posted by USER1 on PICTURE2
5 comments posted by USER2 on PICTURE2

6 comments posted by USER2 on PICTURE3

到目前为止我所拥有的是

SELECT 
users.uid
FROM users
INNER
    JOIN photos
    ON photos.uid = users.uid
INNER
    JOIN comments
    ON comments.iid = photos.iid

这是沙盒测试

http://sqlfiddle.com/#!2/955d5/1

但我不知道接下来该做什么，任何帮助都将不胜感激！除了MySQL之外的任何语言都应该可以工作！

Answer 1

您的查询可能如下：

SELECT users.uid AS UserId, count(comments.cid) AS CountComments
FROM users
INNER
    JOIN photos
    ON photos.uid = users.uid
INNER
    JOIN comments
    ON comments.iid = photos.iid
group by users.uid

你可以test it

如果您想添加图片ID，可以将photo.iid添加到

分组

SELECT users.uid AS UserId, count(comments.cid) AS CountComments, 
  photos.iid as PhotoId
  FROM users
INNER
    JOIN photos
    ON photos.uid = users.uid
INNER
    JOIN comments
    ON comments.iid = photos.iid
group by users.uid, photos.iid

Check it out

Answer 2

SELECT count(*) AS comment_amount, users.uid AS by_user, photos.iid AS on_picture
FROM users
INNER
    JOIN photos
    ON photos.uid = users.uid
INNER
    JOIN comments
    ON comments.iid = photos.iid
group by users.uid, photos.iid

或只是

SELECT count(*) AS comment_amount, uid AS by_user, iid AS on_picture
FROM comments

如果您只需要评论表中的数据

Answer 3

我会首先进行GROUP：

SELECT  iid, uid, count(*)
FROM comments
GROUP BY  iid, uid

之后加入相关表格。

检索数据的3个表的特定JOIN

3 个答案: