MySql如何在该表中基于组更新表？

Question

当我运行以下查询时，我得到了

  

错误＃1093 - 您无法在FROM子句

中为更新指定目标表'x2'

update contacts 
set duplicates = 1
where email in ( select email from contacts 
    group by email
    having count(*) > 1)

任何帮助都将不胜感激。

Answer 1

我认为你可以通过嵌套子查询来欺骗它。

update contacts set duplicates = 1 where email in 
(select email 
  from  
    (select email from contacts group by email having count(*) > 1) as a)

Answer 2

您可以通过JOIN查找具有相同电子邮件和不同主键的其他行。

例如，假设您的主键名为id：

UPDATE contacts AS c1
JOIN contacts AS c2 ON (c1.email = c2.email AND c1.id <> c2.id)
SET c1.duplicates = 1;