一条语句中的两个内部联接产生0结果

Question

当运行多个内部联接时，我得到的结果为零

代码如下所示：

SELECT doubles_ladder.*, players.*
from doubles_ladder
JOIN players on doubles_ladder.player_number = players.Player_number
JOIN players AS play ON doubles_ladder.player_number2 = players.Player_number

我知道这两个表中都有信息，奇怪的是它没有产生结果。

非常感谢您的帮助。

Answer 1

您没有使用为第二个联接表(play(设置的别名。我会在以下方面进行更改：

SELECT doubles_ladder.*, player1.*, player2.*
FROM doubles_ladder
INNER JOIN players AS player1
ON (doubles_ladder.player_number = player1.Player_number)
INNER JOIN players AS player2
ON (doubles_ladder.player_number2 = player2.Player_number)

Answer 2

您正在为doubles_ladder.player_number = players.Player_number和doubles_ladder.player_number2 = players.Player_number的结果进行选择。所有这样的行都具有CCD_ 4。这似乎不是你想要的，而且似乎不会有任何这样的结果。

我想你想要这个，相反：

SELECT doubles_ladder.*, players.*
from doubles_ladder
JOIN players on doubles_ladder.player_number = players.Player_number
JOIN players AS play ON doubles_ladder.player_number2 = play.Player_number