Discription：Write a SQL query to delete all duplicate email entries in a table named Person, keeping only unique emails based on its smallest Id.

删除重复的Email地址，保留Id最小的那个。

使用自身连接循环即可。

# Write your MySQL query statement below

delete p1 from Person p1, Person p2

where p1.Email=p2.Email and p1.Id>p2.Id;

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