Leetcode Problem 1241. Number of Comments per Post

1241. Number of Comments per Post

Leetcode Solutions

Select the sub_id from the Submissions table where parent_id is NULL. This will give us the unique post IDs.
Perform a LEFT JOIN on the Submissions table with itself, joining on the condition that the sub_id of the first instance (representing a post) matches the parent_id of the second instance (representing a comment).
Use COUNT(DISTINCT ...) to count the unique sub_id of comments for each post, ensuring that duplicate comments are only counted once.
Group the results by the sub_id of the posts.
Order the final result by post_id in ascending order.


erDiagram
    Submissions {
        int sub_id PK
        int parent_id
    }

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