8/16 每日一題(MYSQL 刪除重複信箱,刪除其中ID編號較大的)

 Table: Person

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| id          | int     |
| email       | varchar |
+-------------+---------+
id is the primary key (column with unique values) for this table.
Each row of this table contains an email. The emails will not contain uppercase letters.

 

Write a solution to delete all duplicate emails, keeping only one unique email with the smallest id.

For SQL users, please note that you are supposed to write a DELETE statement and not a SELECT one.

For Pandas users, please note that you are supposed to modify Person in place.

After running your script, the answer shown is the Person table. The driver will first compile and run your piece of code and then show the Person table. The final order of the Person table does not matter.

The result format is in the following example.

 

Example 1:

Input: 
Person table:
+----+------------------+
| id | email            |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
| 3  | john@example.com |
+----+------------------+
Output: 
+----+------------------+
| id | email            |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
+----+------------------+
Explanation: john@example.com is repeated two times. We keep the row with the smallest Id = 1.

# Write your MySQL query statement below

DELETE A FROM Person AS A, Person AS B

#刪除Person稱為A表,b 也同樣是Person表 ,稱為B

WHERE A.email=B.email and A.id > B.id

#篩選出其中 A的ID大於B的ID

--------------------------------------------------

# Write your MySQL query statement below select e.id,e.email from (select id,email,rank() over(partition by email order by id) as rnk from Person)e where e.rnk = 1 order by id;

---------------------------------

# Please write a DELETE statement and DO NOT write a SELECT statement.
# Write your MySQL query statement below
delete 
from Person 
where id not in (select id from (select min(id) as id  from Person
 group by email) as t)



#  DELETE FROM Person
# WHERE id NOT IN (
#   SELECT id FROM (
#     SELECT MIN(id) AS id FROM Person GROUP BY email
#   ) AS t
# );