DuplicateEmails
Write a SQL query to find all duplicate emails in a table named Person. +----+---------+ | Id | Email | +----+---------+ | 1 | a@b.com | | 2 | c@d.com | | 3 | a@b.com | +----+---------+ For example, your query should return the following for the above table: +---------+ | Email | +---------+ | a@b.com | +---------+ Note: All emails are in lowercase. 主要是group by的应用 select Email from ( select Email,count(Email) as cnt from Person group by Email ) t where cnt>1; 或者 select Email from ( select Email,count(Email) as cnt from Person group by Email having cnt>1) t ; order by 要在group by 之后使用,不能在group by之前使用。 select Email from ( select Email,count(Email) as cnt from Person order by Email group by Email ) t where cnt>1; 这个执行会有问题。
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