Используя схему OracleHR с ее таблицами следует написать запрос на языке SQL, который позволит получить количество департаментов в котором есть сотрудники из таблицы Employees.

SELECT COUNT (COUNT (*)) COUNT (*) FROM employees WHERE department_id IS NOT NULL GROUP BY department_id;
SELECT COUNT (COUNT (*)) department FROM employees WHERE department_id IS NOT NULL GROUP BY department_id;
SELECT COUNT (COUNT (*)) department_count FROM employees WHERE department_id IS NOT NULL GROUP BY department_count;
SELECT COUNT (COUNT (*)) department_count FROM employees WHERE department_id IS NOT NULL GROUP BY department_id;
SELECT COUNT (COUNT (*)) department_count FROM employees WHERE department_id IS NULL GROUP BY department_id;
SELECT COUNT (COUNT (*)) department_count FROM employees WHERE department_id IS NULL GROUP BY department_id;
SELECT COUNT (COUNT (*)) department_count WHERE department_id IS NOT NULL GROUP BY department_id;
UPDATE COUNT (COUNT (*)) department FROM employees WHERE department_id IS NULL GROUP BY department_id;

Для просмотра статистики ответов нужно войти.