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PracHub provides an interactive SQL console where you can write and test queries against real database schemas. Get instant feedback and compare your solution with the expected output.

What difficulty level is this coding question?

This is a medium difficulty Data Manipulation (SQL/Python) question, commonly asked during Technical Screen rounds at Meta.

What role is this question designed for?

This question is commonly asked for Data Scientist candidates at Meta during technical interviews.

Posts and Replies Engagement | Meta SQL Question

Quick Overview

This question tests practical SQL skills, specifically the use of LEFT JOIN and aggregate functions to compute engagement metrics across relational tables. It evaluates a data scientist's ability to handle zero-count rows and filter results using set-based logic, competencies commonly assessed in data manipulation interviews.

Posts and Replies Engagement

Company: Meta

Role: Data Scientist

Category: Data Manipulation (SQL/Python)

Difficulty: medium

Interview Round: Technical Screen

## Posts and Replies Engagement A content platform stores user-generated **posts** and the **replies** that those posts receive. You need to answer two questions about reply engagement. ### Tables **`posts`** | column | type | description | |-------------|-------------|----------------------------------------------| | `post_id` | INTEGER | Primary key. Unique id of the post. | | `author_id` | INTEGER | Id of the user who created the post. | | `created_at`| TIMESTAMP | When the post was created (UTC). | **`replies`** | column | type | description | |-------------|-------------|--------------------------------------------------------------| | `reply_id` | INTEGER | Primary key. Unique id of the reply. | | `post_id` | INTEGER | Foreign key referencing `posts.post_id`. The post replied to.| | `author_id` | INTEGER | Id of the user who wrote the reply. | | `created_at`| TIMESTAMP | When the reply was created (UTC). | Notes / assumptions: - A post may have zero, one, or many replies. - `replies.post_id` always references an existing row in `posts`. - A user may reply to their own post. - All timestamps are in UTC. ### Part 1 — Reply count per post Return every post together with the number of replies it has received. Posts with **zero** replies must still appear, with a reply count of `0`. Output columns, in this exact order: | column | type | description | |---------------|---------|-----------------------------------| | `post_id` | INTEGER | The post id. | | `reply_count` | INTEGER | Number of replies for that post. | Order the result by `reply_count` descending, breaking ties by `post_id` ascending. ### Part 2 — Posts with no replies Return the `post_id` of every post that has received **no replies at all**. Output column: | column | type | description | |-----------|---------|--------------------------------------| | `post_id` | INTEGER | Id of a post that has zero replies. | Order the result by `post_id` ascending.

Quick Answer: This question tests practical SQL skills, specifically the use of LEFT JOIN and aggregate functions to compute engagement metrics across relational tables. It evaluates a data scientist's ability to handle zero-count rows and filter results using set-based logic, competencies commonly assessed in data manipulation interviews.