Question

3059. Find All Unique Email Domains

English Version

题目描述

Table: Emails

+-------------+---------+
| 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 find all unique email domains and count the number of individuals associated with each domain. Consider only those domains that end with .com.

Return _the result table orderd by email domains in _ascending_ order_.

The result format is in the following example.

 

Example 1:

Input: 
Emails table:
+-----+-----------------------+
| id  | email         |
+-----+-----------------------+
| 336 | hwkiy@test.edu    |
| 489 | adcmaf@outlook.com  |
| 449 | vrzmwyum@yahoo.com  |
| 95  | tof@test.edu      |
| 320 | jxhbagkpm@example.org |
| 411 | zxcf@outlook.com    |
+----+------------------------+
Output: 
+--------------+-------+
| email_domain | count |
+--------------+-------+
| outlook.com  | 2   |
| yahoo.com  | 1   |  
+--------------+-------+
Explanation: 
- The valid domains ending with ".com" are only "outlook.com" and "yahoo.com", with respective counts of 2 and 1.
Output table is ordered by email_domains in ascending order.

解法

方法一：使用 SUBSTRING_INDEX 函数 + 分组统计

我们先筛选出所有以 .com 结尾的邮箱，然后使用 SUBSTRING_INDEX 函数提取出邮箱的域名，最后使用 GROUP BY 统计每个域名的个数。

# Write your MySQL query statement below
SELECT SUBSTRING_INDEX(email, '@', -1) AS email_domain, COUNT(1) AS count
FROM Emails
WHERE email LIKE '%.com'
GROUP BY 1
ORDER BY 1;

import pandas as pd


def find_unique_email_domains(emails: pd.DataFrame) -> pd.DataFrame:
  emails["email_domain"] = emails["email"].str.split("@").str[-1]
  emails = emails[emails["email"].str.contains(".com")]
  return (
    emails.groupby("email_domain")
    .size()
    .reset_index(name="count")
    .sort_values(by="email_domain")
  )