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Leetcode 196 Delete Duplicate Emails

2015-06-26 10:35 375 查看
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  |
+----+------------------+


delete a from Person a, Person b
where a.Email = b.Email and a.Id > b.Id
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