Write complex SQL for cohorts and retention

Q: How do I practice SQL interview questions?

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.

Q: What difficulty level is this coding question?

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

Q: What role is this question designed for?

This question is commonly asked for Software Engineer candidates at TikTok during technical interviews.

Question

Given tables users(uid, created_at, country), orders(order_id, uid, amount, created_at, status), and events(uid, ts, event_type, campaign), write one SQL query that outputs, for each month and country:
(
1) new users,
(
2) conversion rate within 7 days of signup,
(
3) 7-day rolling retention (active on day D and again on D+
7),
(
4) GMV excluding refunded/canceled orders, and
(
5) top campaign by last-touch attribution from events. Handle late-arriving events, deduplicate by (uid, ts, event_type), ensure timezone consistency, and document window-function choices.

PracHub · Accepted Answer

This question evaluates advanced SQL and data-engineering competencies such as cohort and retention analysis, deduplication, timezone normalization, last-touch attribution, aggregate revenue calculations, and effective use of window functions in the Data Manipulation (SQL/Python) domain.

Quick Overview

Write complex SQL for cohorts and retention