# Using LEFT JOIN of users to transactions, return user_id and COALESCE(COUNT(t.transaction_id), 0) AS

Canonical URL: <https://datadriven.io/problems/using-left-join-of-users-to-transactions-return-userid-and-1fe6e07b>

Domain: SQL · Difficulty: medium

## Problem

Using LEFT JOIN of users to transactions, return user_id and COALESCE(COUNT(t.transaction_id), 0) AS tx_count (users with no transactions get 0). Group by user_id. Order by tx_count ASC, user_id.

## Related

- [All practice problems](https://datadriven.io/problems)
- [Mock interview mode](https://datadriven.io/interview/using-left-join-of-users-to-transactions-return-userid-and-1fe6e07b)
- [SQL Interview Questions](https://datadriven.io/sql-interview-questions)
- [Data Engineering Interview Prep Guide](https://datadriven.io/data-engineer-interview-prep)
- [Daily Challenge](https://datadriven.io/daily)

---

Source: DataDriven (https://datadriven.io). 100% free data engineering interview prep. Live code execution against Postgres 16, Python 3.11, and Spark sandboxes. No paywall, no premium tier, no signup gate.