MySQL的：不顯示結果爲NULL LEFT JOIN /分辯

Question

我以這種方式完成的：

SELECT * FROM ( 
       SELECT DISTINCT (u2.email) email FROM `users` u1 LEFT JOIN 
         users u2 ON u1.email = u2.email AND u1.id <> u2.id 
       )users WHERE email IS NOT NULL 

是否有合同公式？

Answer 1

如果您不想要NULL結果，請使用INNER JOIN。

SELECT DISTINCT(u2.email) FROM users u1 
    INNER JOIN users u2 ON u1.email = u2.email AND u1.id <> u2.id 

如果你必須使用LEFT JOIN：

SELECT DISTINCT(u2.email) FROM users u1 
    LEFT JOIN users u2 ON u1.email = u2.email AND u1.id <> u2.id 
    WHERE u2.email IS NOT NULL