Group by. Используем группировку вместе с аггрегатными функциями

create table customers ( id integer constraint customers_pk primary key autoincrement, name varchar(255), age integer, country varchar (255) ); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Leopoldo Moore', '25', 'Belarus'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Laura Ortiz', '41', 'USA'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Eda OHara', '58', 'Russia'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Sibyl Gibson', '49', 'India'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Dr. Clovis Emmerich II', '52', 'USA'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Mathilde Schaefer', '55', 'China'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Maegan Green', '49', 'USA'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Mrs. Ines Turcotte', '48', 'China'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Dr. Alexandro Ryan III', '41', 'Belarus'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Ryann Kulas', '27', 'India'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Viola Schaden', '39', 'Belarus'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Haley Beatty', '21', 'India'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Gonzalo Dach', '60', 'India'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Marlene Gutkowski', '30', 'China'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Prof. Easton Toy', '25', 'Russia'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Camren Koelpin', '65', 'Belarus'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Stephon Kulas', '37', 'Russia'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Jeanne Zboncak', '40', 'Belarus'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Kari Daugherty', '54', 'India'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Mellie Hagenes Sr.', '18', 'USA'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Jamar Hagenes', '57', 'Belarus'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Christ OConner', '21', 'Russia'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Sanford Bergnaum', '33', 'Germany'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Prof. Zachery Bernhard III', '51', 'Germany'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Bridie Torphy', '24', 'India'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Christelle Murray', '22', 'India'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Dr. Lera Conn', '33', 'China'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Taya Bergnaum', '55', 'Germany'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Lolita Raynor', '57', 'Belarus'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Meta Kub IV', '48', 'Russia'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Bernita West', '34', 'China'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Abdiel Huels', '30', 'Germany'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Brando Becker', '50', 'Germany'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Dr. Grover Runte DVM', '19', 'Germany'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Kellie Barrows', '21', 'Russia'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Sammie Crona', '61', 'India'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Prof. Steve Dach', '39', 'India'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Cathryn Koelpin', '20', 'Russia'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Susanna Crooks', '51', 'India'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Prof. Arlene Rolfson', '22', 'USA'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Mrs. Sharon Ortiz', '52', 'Russia'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Dr. Allen Corkery IV', '39', 'India'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Lina Bernhard', '22', 'Germany'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Vincenza Willms MD', '64', 'Germany'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Alycia Donnelly IV', '49', 'Russia'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Dr. Ignatius Pacocha IV', '51', 'India'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Sammie Bayer', '23', 'USA'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Miss Muriel Murphy DDS', '18', 'India'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Shawna Klocko Jr.', '55', 'China'); INSERT INTO customers (`name`, `age`, `country`) VALUES ('Beaulah Kerluke', '29', 'Belarus');