SQL：如何从同一个表中选择两个ID作为两个名称？

Question

我是新来的SQL，并试图获得连接和引用的句柄。

数据库是这样的：

玩家

id | name 
----+------- 
    1 | john 
    2 | tim 
    3 | frank 
    4 | tony 
    5 | mark 

匹配

id | winner | loser 
----+--------+------- 
    1 |  2 |  4 
    2 |  3 |  4 
    3 |  4 |  5 
    4 |  1 |  4 

我想要得到这样的结果：

id | winner | loser 
----+--------+------- 
    1 | tim | tony 
    2 | frank | tony 
    3 | tony | mark 
    4 | john | tony 

到目前为止，我可以这样做：

select matches.id, players.name as winner, players.name as loser 
    from matches, players 
    where winner = players.id; 

但是，如果我添加and loser = players.id，它不返回行。

我也试过这样：

select matches.id, players.name as winner, players.name as loser 
    from matches 
    join players on matches.winner = players.id 
    join players on matches.loser = players.id; 

产生ERROR: table name "players" specified more than once。

我把这个搜索了一个小时，可以找到很多的案例，几乎得到我想要的，但我仍然无法弄清楚如何用同一个表中的两个名称替换两个ID。

Answer 1

你几乎有：

select matches.id, w.name as winner, l.name as loser 
from matches 
join players w on matches.winner = w.id 
join players l on matches.loser = l.id; 

Answer 2

您需要别名表的名称，以便您可以指定加入的数据应该来自。

select 
    matches.id, 
    p1.name as winner, 
    p2.name as loser 
from matches 
    join players p1 on matches.winner = p1.id 
    join players p2 on matches.loser = p2.id; 

Answer 3

您将希望确保您在该表上连接两次并保持别名正确。

SELECT Matches.id, winner.name, loser.name 
From Matches 
INNER JOIN Players as winner on winner.id = Matches.winner 
INNER JOIN Players as loser on loser.id = Matches.winner;