Question

我需要加入2个表，但这些表有两对需要连接的键。

ID，Car和Color是一个“对”而不是OTHERID。

LEFT JOIN TableTest t2 ON
    (t1.ID = t2.ID)
    AND
    (t1.CAR = t2.CAR)
    AND (t1.Color = t2.Color)

我现在尝试将OTHERID键添加到语句中：

LEFT JOIN TableTest t2 ON
    (t1.ID = t2.ID)
    AND
    (t1.CAR = t2.CAR)
    AND
    (t1.Color = t2.Color)
    OR
    (t1.OTHERID = t2.OTHERID);

但那不起作用。

Answer 1

您忽略了AND vs OR的运算符优先级。

如果t1.OTHERID = t2.OTHERID应该首先出现，那么就这样推广它（你也不需要为每个表达式加上括号）：

LEFT JOIN TableTest t2 ON
    t1.OTHERID = t2.OTHERID
    OR
    (
        t1.ID = t2.ID
        AND
        t1.CAR = t2.CAR
        AND
        t1.Color = t2.Color
    );

Answer 2

小心括号。

LEFT JOIN TableTest t2 ON (t1.ID = t2.ID AND t1.CAR = t2.CAR AND t1.Color = t2.Color) OR t1.OTHERID = t2.OTHERID

加入2个不同的钥匙

2 个答案: