Compute High-Call Usage Rates

A voice-calling product keeps two tables. users stores user_id (BIGINT) and country_code (STRING), while calls stores call_id (BIGINT), caller_id (BIGINT), recipient_id (BIGINT) and started_at (TIMESTAMP). Both caller_id and recipient_id reference users.user_id. Every calls row stands for one genuine completed call, and all started_at values are written in UTC. Day-level grouping must follow the Europe/London calendar; report_date is such a London calendar day. Produce…