# 1241. Number of Comments per Post

https://leetcode.com/problems/number-of-comments-per-post

## Description

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.
```

## ac

```java
```
