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Create table Person (id int, name varchar(15), phone_number varchar(11)); Create table Country (name varchar(15), country_code varchar(3)); Create table Calls (caller_id int, callee_id int, duration int); insert into Person (id, name, phone_number) values ('3', 'Jonathan', '051-1234567'); insert into Person (id, name, phone_number) values ('12', 'Elvis', '051-7654321'); insert into Person (id, name, phone_number) values ('1', 'Moncef', '212-1234567'); insert into Person (id, name, phone_number) values ('2', 'Maroua', '212-6523651'); insert into Person (id, name, phone_number) values ('7', 'Meir', '972-1234567'); insert into Person (id, name, phone_number) values ('9', 'Rachel', '972-0011100'); insert into Country (name, country_code) values ('Peru', '051'); insert into Country (name, country_code) values ('Israel', '972'); insert into Country (name, country_code) values ('Morocco', '212'); insert into Country (name, country_code) values ('Germany', '049'); insert into Country (name, country_code) values ('Ethiopia', '251'); insert into Calls (caller_id, callee_id, duration) values ('1', '9', '33'); insert into Calls (caller_id, callee_id, duration) values ('2', '9', '4'); insert into Calls (caller_id, callee_id, duration) values ('1', '2', '59'); insert into Calls (caller_id, callee_id, duration) values ('3', '12', '102'); insert into Calls (caller_id, callee_id, duration) values ('3', '12', '330'); insert into Calls (caller_id, callee_id, duration) values ('12', '3', '5'); insert into Calls (caller_id, callee_id, duration) values ('7', '9', '13'); insert into Calls (caller_id, callee_id, duration) values ('7', '1', '3'); insert into Calls (caller_id, callee_id, duration) values ('9', '7', '1'); insert into Calls (caller_id, callee_id, duration) values ('1', '7', '7'); WITH data AS ( SELECT c.name AS country, AVG(cl.duration) OVER (PARTITION BY c.name) AS country_avg, AVG(cl.duration) OVER () AS total_avg FROM Country c JOIN Person p ON c.country_code = SUBSTR(p.phone_number, 1, 3) JOIN Calls cl ON cl.caller_id = p.id OR cl.callee_id = p.id ) SELECT DISTINCT country FROM data WHERE country_avg > total_avg ; -- For check WITH data AS ( SELECT c.name AS country, c.country_code, p.id, p.name as Person, p.phone_number, AVG(cl.duration) OVER (PARTITION BY c.name) AS country_avg, AVG(cl.duration) OVER () AS total_avg FROM Country c JOIN Person p ON c.country_code = SUBSTR(p.phone_number, 1, 3) JOIN Calls cl ON cl.caller_id = p.id OR cl.callee_id = p.id ) SELECT * FROM data ;