refactor 1241

Author: fishercoder1534

database/_1241.sql

@@ -1,62 +1,3 @@
---1241. Number of Comments per Post
---
---Table: Submissions
---
---+---------------+----------+
---| Column Name   | Type     |
---+---------------+----------+
---| sub_id        | int      |
---| parent_id     | int      |
---+---------------+----------+
---There is no primary key for this table, it may have duplicate rows.
---Each row can be a post or comment on the post.
---parent_id is null for posts.
---parent_id for comments is sub_id for another post in the table.
---
---
---Write an SQL query to find number of comments per each post.
---
---Result table should contain post_id and its corresponding number_of_comments, and must be sorted by post_id in ascending order.
---
---Submissions may contain duplicate comments. You should count the number of unique comments per post.
---
---Submissions may contain duplicate posts. You should treat them as one post.
---
---The query result format is in the following example:
---
---Submissions table:
---+---------+------------+
---| sub_id  | parent_id  |
---+---------+------------+
---| 1       | Null       |
---| 2       | Null       |
---| 1       | Null       |
---| 12      | Null       |
---| 3       | 1          |
---| 5       | 2          |
---| 3       | 1          |
---| 4       | 1          |
---| 9       | 1          |
---| 10      | 2          |
---| 6       | 7          |
---+---------+------------+
---
---Result table:
---+---------+--------------------+
---| post_id | number_of_comments |
---+---------+--------------------+
---| 1       | 3                  |
---| 2       | 2                  |
---| 12      | 0                  |
---+---------+--------------------+
---
---The post with id 1 has three comments in the table with id 3, 4 and 9. The comment with id 3 is repeated in the table, we counted it only once.
---The post with id 2 has two comments in the table with id 5 and 10.
---The post with id 12 has no comments in the table.
---The comment with id 6 is a comment on a deleted post with id 7 so we ignored it.
---
---# Write your MySQL query statement below
-
 select s.sub_id as post_id,
 (select count(distinct(s1.sub_id)) from Submissions s1 where s1.parent_id = s.sub_id) as number_of_comments
 from Submissions s