从另一个表中的一个表加入多个列到单个列

Question

我想了解如何将一个表中的多个列连接到另一个表中的单个列。

这是最简单的形式我的表结构：

队

id | team_name | 
1 | teamA | 
2 | teamB | 
3 | teamC | 
4 | teamD | 

交易

id | team_1 (FK to teams.id) | team_2 (FK to teams.id) | 
1 |   1    |    2   | 
2 |   3    |    4   | 

这是我当前的SQL它连接到trades.team_1队。编号：

SELECT teams.team_name AS team1, teams.team_name AS team2, trades.team_1, trades.team_2 
FROM teams 
JOIN trades ON (trades.team_1 = teams.id); 

我的问题是，如何创建第二个连接，也将trades.team_2连接到trades.id？

这将意味着trades.team_1和trades.team_2将被加入到trades.id

结果我想回去是：

team1 | team2 | team_1 | team_2 | 
teamA | teamB | 1  |  2 | 
teamC | teamD | 3  |  4 | 

Answer 1

像这样：

select t1.team_name as team1, t2.team_name as team2, t.team_1, t.team_2 
from trades t 
inner join teams t1 on t1.id = t.team_1 
inner join teams t2 on t2.id = t.team_2; 

Answer 2

你需要加入两次：

SELECT t1.team_name as team1, t2.team_name as team2, trades.team_t, trades.team_2 
FROM teams t1, teams t2, trades 
WHERE t1.id = trades.team_1 and t2.id = trades.team_2 

Answer 3

再次尝试加入团队表，但使用两种不同的别名：

SELECT 
    teams1.team_name AS team1, 
    teams2.team_name AS team2, 
    trades.team_1, 
    trades.team_2 
FROM trades 
JOIN teams AS teams1 ON trades.team_1 = teams1.id 
JOIN teams AS teams2 ON trades.team_2 = teams2.id 

Answer 4

SELECT t1.team_name AS team1, t2.team_name AS t2, tr.team_1, tr.team_2 
FROM trades tr 
INNER JOIN teams t1 ON t1.id = tr.team_1 
INNER JOIN teams t2 ON t2.id = tr.team_2