Write a SQL query to delete all duplicate email entries in a table named Person,
keeping only unique emails based on its smallest Id.
+----+------------------+ | Id | Email | +----+------------------+ | 1 | john@example.com | | 2 | bob@example.com | | 3 | john@example.com | +----+------------------+ Id is the primary key column for this table.
For example, after running your query, the above Person table should have
the following rows:
+----+------------------+ | Id | Email | +----+------------------+ | 1 | john@example.com | | 2 | bob@example.com | +----+------------------+如果这样写会有错：
delete from Person where id not in (select max(a.id) as id from Person a group by email);
| Runtime Error Message: | You can‘t specify target table ‘Person‘ for update in FROM clause |
| Last executed input: | {"headers": {"Person": ["Id", "Email"]}, "rows": {"Person": []}} |
delete from Person where id not in (select id as id from (select min(b.id) as id from Person b group by email) as a);
LeetCode Delete Duplicate Emails
原文：http://blog.csdn.net/u012925008/article/details/45008941