题目:
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 | [email protected] |
| 2 | [email protected] |
| 3 | [email protected] |
+—-+——————+
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 | [email protected] |
| 2 | [email protected] |
+—-+——————+
Answer:
思路:使用DELETE FROM
,注意用MAX
找出最大的id
不行,因为有多组重复的情况。
# Write your MySQL query statement below
DELETE A1
FROM
person AS A1,
person AS A2
WHERE
A1.Email = A2.Email
AND A1.Id > A2.Id