Leetcode: find all duplicate

1640 단어

Leetcode : Duplicate Emails


Write a SQL query to find all duplicate emails in a table named Person. +—-+———+ | Id | Email | +—-+———+ | 1 | [email protected] | | 2 | [email protected] | | 3 | [email protected] | +—-+———+ For example, your query should return the following for the above table: +———+ | Email | +———+ | [email protected] | +———+

Method:


Use count() group by Email.
select Email from ( select count(*) as c, Email from Person group by Email ) as a where c > 1;

Add ORDER in subquery. That will accelerate the parent query.
select Email from ( select count(*) as c, Email from Person group by Email order by c ) as a where c > 1;

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