Shared Channel Contacts

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

Domain

SQL

Difficulty

hard

Seniority

senior

Problem

Using our chat message data, build a contact overlap picture. For each sender, count how many other unique senders share at least one channel with them. Show each sender and their shared contact count, sorted from most contacts to least.

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.