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1729. Find Followers Count
Level
Easy
Description
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 following relationship 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:
Followers table:
+---------+-------------+
| user_id | follower_id |
+---------+-------------+
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 2 | 1 |
+---------+-------------+
Result table:
+---------+----------------+
| user_id | followers_count|
+---------+----------------+
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
+---------+----------------+
The followers of 0 are {1}
The followers of 1 are {0}
The followers of 2 are {0,1}
Solution
For each user_id, count the number of entries in Followers. Group the result by user_id and order the result by user_id.
# Write your MySQL query statement below
select user_id, count(*) as followers_count from Followers
group by user_id
order by user_id;