Question

196. 删除重复的电子邮箱

English Version

题目描述

表: Person

+-------------+---------+
| Column Name | Type  |
+-------------+---------+
| id      | int   |
| email     | varchar |
+-------------+---------+
id 是该表的主键列(具有唯一值的列)。
该表的每一行包含一封电子邮件。电子邮件将不包含大写字母。

 

编写解决方案 删除 所有重复的电子邮件，只保留一个具有最小 id 的唯一电子邮件。

（对于 SQL 用户，请注意你应该编写一个 DELETE 语句而不是 SELECT 语句。）

（对于 Pandas 用户，请注意你应该直接修改 Person 表。）

运行脚本后，显示的答案是 Person 表。驱动程序将首先编译并运行您的代码片段，然后再显示 Person 表。Person 表的最终顺序 无关紧要 。

返回结果格式如下示例所示。

 

示例 1:

输入: 
Person 表:
+----+------------------+
| id | email      |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
| 3  | john@example.com |
+----+------------------+
输出: 
+----+------------------+
| id | email      |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
+----+------------------+
解释: john@example.com重复两次。我们保留最小的Id = 1。

解法

方法一

import pandas as pd


# Modify Person in place
def delete_duplicate_emails(person: pd.DataFrame) -> None:
  # Sort the rows based on id (Ascending order)
  person.sort_values(by="id", ascending=True, inplace=True)
  # Drop the duplicates based on email.
  person.drop_duplicates(subset="email", keep="first", inplace=True)

# Write your MySQL query statement below
DELETE FROM Person
WHERE id NOT IN (SELECT MIN(id) FROM (SELECT * FROM Person) AS p GROUP BY email);

方法二

# Write your MySQL query statement below
DELETE FROM Person
WHERE
  id NOT IN (
    SELECT id
    FROM
      (
        SELECT
          id,
          ROW_NUMBER() OVER (
            PARTITION BY email
            ORDER BY id
          ) AS rk
        FROM Person
      ) AS p
    WHERE rk = 1
  );

方法三

DELETE p2
FROM
  person AS p1
  JOIN person AS p2 ON p1.email = p2.email
WHERE
  p1.id < p2.id;