코딩테스트 SQL 코드카타 (Followers count)

문제

Find Followers Count - LeetCode

 

Write a solution that will, for each user, return the number of followers.

Return the result table ordered by user_id in ascending order.

The result format is in the following example.

 

Example 1:

Input: 
Followers table:
+---------+-------------+
| user_id | follower_id |
+---------+-------------+
| 0       | 1           |
| 1       | 0           |
| 2       | 0           |
| 2       | 1           |
+---------+-------------+
Output: 
+---------+----------------+
| user_id | followers_count|
+---------+----------------+
| 0       | 1              |
| 1       | 1              |
| 2       | 2              |
+---------+----------------+
Explanation: 
The followers of 0 are {1}
The followers of 1 are {0}
The followers of 2 are {0,1}

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풀이

1. user_id 당 follower_id 카운트
2. user_id 그룹화
3. user_id 기준오름정렬

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코드

select user_id, count(follower_id) as followers_count
from Followers
group by user_id
order by user_id

 

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링크

LeetCode/1729-find-followers-count at main · K-MarkLee/LeetCode

LeetCode/1729-find-followers-count at main · K-MarkLee/LeetCode