Используя схему OracleHR с ее таблицами следует написать запрос на языке SQL, который позволит получить список сотрудников которые живут в Europe (region_name) из таблиц Employees, Departaments, Locations, Countries, Regions.

SELECT first_name FROM employees JOIN departments USE (department_id) JOIN locations USE (location_id) JOIN countries USE (country_id) JOIN regions USE (region_id) WHERE region_name = 'Europe';
SELECT first_name FROM employees JOIN departments USE (department_id) JOIN locations USE (location_id) JOIN countries USE (country_id) JOIN regions USE (region_id) WHERE region_name = 'Europe';
SELECT first_name FROM employees JOIN departments USING (department_id) JOIN locations USING (location_id) JOIN countries USING (country_id) JOIN regions USING (region_id) WHERE region_name = 'Europe';
SELECT first_name FROM employees SPLIT departments USING (department_id) SPLIT locations USING (location_id) SPLIT countries USING (country_id) SPLIT regions USING (region_id) WHERE region_name = 'Europe';
SELECT first_name FROM employees e JOIN departments d OFF (e.department_id = d.department_id) JOIN locations l OFF (d.location_id = l.location_id) JOIN countries c OFF (l.country_id = c.country_id) JOIN regions r OFF (c.region_id = r.region_id) WHERE region_name = 'Europe';
SELECT first_name FROM employees e JOIN departments d ON (e.department = d.department) JOIN locations l ON (d.location = l.location) JOIN countries c ON (l.country = c.country) JOIN regions r ON (c.region = r.region) WHERE region_name = 'Europe';
SELECT first_name FROM employees e JOIN departments d ON (e.department_id = d.department_id) JOIN locations l ON (d.location_id = l.location_id) JOIN countries c ON (l.country_id = c.country_id) JOIN regions r ON (c.region_id = r.region_id) WHERE region_name = 'Europe';
SELECT first_name FROM employees e SPLIT departments d ON (e.department_id = d.department_id) SPLIT locations l ON (d.location_id = l.location_id) SPLIT countries c ON (l.country_id = c.country_id) SPLIT regions r ON (c.region_id = r.region_id) WHERE region_name = 'Europe';

К сожалению, у нас пока нет статистики ответов на данный вопрос, но мы работаем над этим.