LeetCode-in-Java
1729. Find Followers Count
Easy
SQL Schema
Table: Followers
+-------------+------+
| Column Name | Type |
+-------------+------+
| user_id | int |
| follower_id | int |
+-------------+------+
(user_id, follower_id) is the primary key for this table.
This table contains the IDs of a user and a follower in a social media app where the follower follows the user.
Write an SQL query that will, for each user, return the number of followers.
Return the result table ordered by user_id.
The query 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}
Solution
# Write your MySQL query statement below
select user_id, count(follower_id) as followers_count
from followers
group by user_id
order by user_id