Question

我有2个表，users和players

在表格users中，我有列userid和username。在表格players中，我有列id，player1和player2。列id是自动增量主键。 player1和player2都是表userid中users的外键

我尝试在同一行中同时拥有player1和player2个用户名的联接。例如，userid 4有username Sam，userid 6有username Kevin。这只是一行查询结果的一个例子：

player1  username  player2  username
------------------------------------
   4        Sam       6       Kevin

Answer 1

只要每次都有唯一的别名，就可以多次加入一个表：

select p1.userid, p1.username, p2.userid, p2.username
from players p
join users p1 on p.player1 = p1.userid
join users p2 on p.player2 = p2.userid
where ...

Answer 2

SELECT Player1, u1.UserName, Player2, u2.UserName
FROM Players, Users u1, Users u2
WHERE Player1=u1.userid and
Player2=u2.userid

Answer 3

select a.userid, a.username, b.userid, b.username from players p join users a on p.player1 = a.userid join users b on p.player2 = b.userid where -------

Answer 4

试试这个

从中选择res1.player1，res1.user_name，res2.player1，res2.user_name （SELECT * FROM test_player作为t1内部联接test_user为t2 on t1。player1 = t2.user_id）为res1，（SELECT * FROM test_player为t1 内联接test_user为t1上的t2。player2 = t2.user_id）为res2

如何执行简单的连接

4 个答案: