Question

如何在以下查询中找到重复的电子邮件？

SELECT b_email AS email FROM user WHERE status = 3 AND b_email != '' 
UNION (SELECT c_email AS email FROM user WHERE status = 3 AND c_email != '') 
UNION (SELECT user_email AS email FROM user WHERE status = 3 AND user_email != '') 
UNION (SELECT user_email AS email FROM sub_user WHERE status = 3 AND user_email != '') 
UNION (SELECT su_email AS email FROM sub_user WHERE status = 3 AND su_email != '') 
ORDER BY email ASC

感谢。

Answer 1

您的查询结果不会重复，因为UNION会删除重复项。要保留重复项，请改为使用UNION ALL：

SELECT b_email AS email FROM user WHERE status = 3 AND b_email != ''
UNION ALL SELECT c_email AS email FROM user WHERE status = 3 AND c_email != ''
...

要确定哪些电子邮件地址重复，您可以执行以下操作：

更改您的查询以返回所有电子邮件地址列表，包括重复项（这意味着使用UNION ALL代替UNION）
使用通过电子邮件地址计算的外部查询
将外部查询结果限制为计数为两个或更多的电子邮件地址

以下是如何操作（注意这假设您发布的查询有效）：

SELECT email, COUNT(*)
FROM (
  SELECT b_email AS email FROM user WHERE status = 3 AND b_email != '' 
  UNION ALL SELECT c_email AS email FROM user WHERE status = 3 AND c_email != ''
  UNION ALL SELECT user_email AS email FROM user WHERE status = 3 AND user_email != ''
  UNION ALL SELECT user_email AS email FROM sub_user WHERE status = 3 AND user_email != ''
  UNION ALL SELECT su_email AS email FROM sub_user WHERE status = 3 AND su_email != ''
) EmailGlom
GROUP BY email
HAVING COUNT(*) > 1

您的结果将是在内部查询中多次显示的每个电子邮件地址。

MySQL在UNION表中查找重复的行

1 个答案: