如何在MySQL中进行正确的外连接？

Question

'SELECT * FROM (SELECT * FROM t1 
      RIGHT OUTER JOIN t2 ON t1.wid = t2.wid 
      WHERE t2.wid IS NULL) 
      LIMIT ' . $number; 

此SQL行不会给出一行，我不知道原因。 t1满了行，而t2是空表。

Answer 1

既然你需要做一个LEFT OUTER JOIN检索排在t1

您还需要避免重复的列名在内部结果你让外部选择之前，如SELECT t1.*

你也可能需要给一个别名派生表内选择，例如，t3 ...

SELECT t3.* FROM (
    SELECT t1.* FROM t1 
    LEFT OUTER JOIN t2 ON t1.wid = t2.wid 
    WHERE t2.wid IS NULL) 
AS t3;