Question

需要帮助，我有三张桌子＆＃34; USERS＆＃34;，＆＃34; FRIENDS＆＃34;和＆＃34;状态＆＃34;我很难通过＆＃34; FRIENDS TABLE＆＃34;

中的条件加入他们

 users table
id | name | usercode
--------------------
1 | david | 2WM
2 | Samme | E5N
3 | Awudu | C0Q
4 | John  | VX6
5 | Jerem | FG3

Friends Table
id | actor | target
--------------------
1  | E5N   | FG3
2  | 2WM   | VX6
3  | FG3   | 2WM
4  | C0Q   | VX6
5  | FG3   | VX6

 Status Table
id | usercode | status
--------------------
1  | E5N      | I am busy now
2  | 2WM      | The night is falling too fast
3  | FG3      | Good day
4  | C0Q      | Very tired, trust me
5  | VX6      | YeLLLLOOO

我希望得到的是所有＆＃34;用户＆＃34;来自＆＃34; USERS TABLE＆＃34;及其相应的状态＆＃34;来自＆＃34;状态表＆＃34;谁拥有＆＃39; FG3＆＃39; as＆＃34; target＆＃34;或者＆＃39; FG3＆＃39; as＆＃34;演员＆＃34;来自＆＃34; FRIENDS TABLE＆＃34;

所以结果就像

id | name  | usercode | actor | target | status
------------------------------------------------
 2 | Samme | E5N      | E5N   | FG3    | I am busy now
 1 | david | 2WM      | FG3   | 2WM    | The night is falling too fast
 5 | John  | VX6      | FG3   | VX6    | YeLLLLOOO

请不要错过任何帮助，谢谢。

Answer 1

首先，将您的用户表与friends表连接，然后将状态表与friends表连接

SELECT friend_user.name,
       friend_user.usercode,
       Friends.actor,
       Friends.target,
       friend_status.status
FROM users AS my_user_table
JOIN Friends ON Friends.actor = my_user_table.usercode
JOIN users AS friend_user ON friend_user.usercode = Friends.target
OR friend_user.usercode = Friends.actor
JOIN Status AS friend_status ON friend_status.usercode = friend_user.usercode
WHERE my_user_table.usercode = 'FG3'

Answer 2

SELECT u.name,
       u.usercode,
       f.actor,
       f.target,
       s.status
FROM Users u,
    Friends f,
    Status s 
WHERE ((u.usercode = f.actor AND 'FG3' = f.target)
OR (u.usercode = f.target AND 'FG3' = f.actor)) 
AND s.usercode = u.usercode

三个表上的MySql查询

2 个答案: