The Ninety-Day Comeback

A hard SQL interview practice problem on DataDriven. Write and execute real sql code with instant grading.

Domain

SQL

Difficulty

hard

Seniority

L4

Problem

A user is considered 'retained' if they start at least one additional session strictly after their very first session, but no later than 90 calendar days after that first session. Working from the user_sessions table, treat each user's earliest session_start (by calendar date) as their first session. Calculate the proportion of retained users out of all users who have any session. Return a single retention rate as a REAL value (retained users divided by total users).

Summary

Everyone shows up once. Who comes back before the quarter ends?

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