Monthly Service Retention

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

Domain

SQL

Difficulty

hard

Seniority

senior

Problem

For December 2025 and January 2026, find the percentage of users active in a given month who also appear in any future month. Treat missing future activity as zero retention. Return the service name, month, and retention percentage.

Practice This Problem

Solve this SQL problem with real code execution. DataDriven runs your SQL queries against a live PostgreSQL database and grades it instantly.