CREATE TABLE departments (department_id VARCHAR2)
CREATE TABLE employees (department_id VARCHAR2)

display the department name and number of employees in each of the department.
SELECT department_name, COUNT(*) FROM employees AS T1 JOIN departments AS T2 ON T1.department_id = T2.department_id GROUP BY department_name
SELECT "department_name", COUNT(*) FROM "employees" "T1" JOIN "departments" "T2" ON "T1"."department_id" = "T2"."department_id" GROUP BY "department_name"