Question

我正在尝试加入3个mysql表;朋友，用户和评论。

users:
id  | firstName | lastName
--------------------------
12  | edwin     | leon
9   | oscar     | smith
1   | kasandra  | rios

friends:
userId   | friendID
----------------------
   12    | 9
   9     | 12
   12    | 1
   1     | 12

comments:
commenter | comment  | commentDate
----------------------------
 12       |  hey     | Oct-2
 1        | Hmmmmmm  | Nov-1
 9        | ok       | Nov-2
 9        | testing  | Nov-2
 1        | hello    | Dec-20    
 1        | help     | Dec-20

所以我想要做的就是选择所有用户的朋友的评论。所以我想要输出的是你朋友的评论：例如：

for edwin leon (id 12) it would output this
friendID    | comment  | commentDate | firstName | lastName
-----------------------------------------------------------
   1        | Help     |    Dec-20   | kasandra  | rios
   1        | Hello    |    Dec-20   | kasandra  | rios
   9        | testing  |    Nov-2    | oscar     | smith
   9        | ok       |    Nov-2    | oscar     | smith
   1        | Hmmmm    |    Nov-1    | kasandra  | rios

它会得到所有朋友的评论，但不是他的。这是我的代码：

SELECT friends.friendID, users.firstName, users.lastName, comments.comment, comments.commentDate  
FROM users
  JOIN friends ON friends.userID = users.id
  JOIN comments ON comments.commenter = friends.friendID 
 WHERE users.id = '12' AND comments.commenter != '12'

它确实有效，但不是得到评论者的名字，我得到所有人的edwin leon

Answer 1

您希望将用户表加入friendId而不是userid：

SELECT friends.friendID, users.firstName, users.lastName, comments.comment, comments.commentDate  
FROM users
  JOIN friends ON friends.friendID = users.id
  JOIN comments ON comments.commenter = friends.friendID 
 WHERE friends.userID = '12' AND comments.commenter != '12'

查看在线工作：sqlfiddle

Answer 2

试试这个::

Select friendId, comment, commentdate, firstname, lastname
from
friends inner join comments on (friends.friendId=comenter)
inner join users on (users.id=friends.friendId)
where friends.userid=?

Answer 3

试试这个（我还没有测试过）

SELECT friends.friendID, u2.firstName, u2.lastName, comments.comment, comments.commentDate  
FROM users AS u
  JOIN friends ON friends.userID = u.id
  JOIN comments ON comments.commenter = friends.friendID 
  JOIN users AS u2 ON u2.id = friends.friendID
 WHERE u.id = '12' AND comments.commenter != '12'

Mysql加入更多2个表

3 个答案: