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 | +----+------------------+
需求：删除重复数据，保留ID最小的
DELETE t1 FROM persons t1 LEFT JOIN(
SELECT MIN(Id) Id,Email FROM Persons GROUP BY Email HAVING COUNT(Email)>1
)t2 ON t1.Email=t2.Email
WHERE t1.Id>t2.Id
[LeetCode]-DataBase-Delete Duplicate Emails
原文：http://www.cnblogs.com/lianliang/p/5303057.html