CREATE TABLE employees (employee_id NUMBER, first_name CLOB, last_name CLOB, email CLOB, phone_number CLOB, hire_date TIME, job_id CLOB, salary NUMBER, commission_pct NUMBER, manager_id NUMBER, department_id NUMBER)
CREATE TABLE regions (region_id NUMBER, region_name CLOB)
CREATE TABLE jobs (job_id CLOB, job_title CLOB, min_salary NUMBER, max_salary NUMBER)
CREATE TABLE job_history (employee_id NUMBER, start_date TIME, end_date TIME, job_id CLOB, department_id NUMBER)
CREATE TABLE departments (department_id NUMBER, department_name CLOB, manager_id NUMBER, location_id NUMBER)
CREATE TABLE locations (location_id NUMBER, street_address CLOB, postal_code CLOB, city CLOB, state_province CLOB, country_id CLOB)
CREATE TABLE countries (country_id CLOB, country_name CLOB, region_id NUMBER)

What are the names of departments that have at least one employee.
SELECT DISTINCT T2.department_name FROM employees AS T1 JOIN departments AS T2 ON T1.department_id = T2.department_id
SELECT DISTINCT "T2"."department_name" FROM "employees" "T1" JOIN "departments" "T2" ON "T1"."department_id" = "T2"."department_id"