Problem Description –
A telecommunications company wants to invest in new countries. The company intends to invest in the countries where the average call duration of the calls in this country is strictly greater than the global average call duration.
Write an SQL query to find the countries where this company can invest.
Return the result table in any order.
The query result format is in the following example.
Problem Link – countries to invest
Difficulty Level – Medium
SELECT co.name AS country FROM person p JOIN country co ON SUBSTRING(phone_number,1,3) = country_code JOIN calls c ON p.id IN (c.caller_id, c.callee_id) GROUP BY co.name HAVING AVG(duration) > (SELECT AVG(duration) FROM calls)