Oracle 21c

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CREATE TABLE departments(  department_id, department_name) AS
SELECT 1, 'IT' FROM DUAL UNION ALL
SELECT 3, 'Sales' FROM DUAL UNION ALL
SELECT 2, 'DBA' FROM DUAL;
3 rows affected

CREATE TABLE employees (employee_id, first_name, last_name, hire_date, salary,  department_id) AS
SELECT 1, 'Lisa', 'Saladino', DATE '2001-04-03', 100000, 1 FROM DUAL UNION ALL
SELECT 2, 'Abby', 'Abbott', DATE '2001-04-04', 50000, 1 FROM DUAL UNION ALL
SELECT 3, 'Beth', 'Cooper', DATE '2001-04-05', 60000, 1 FROM DUAL UNION ALL
SELECT 4, 'Carol', 'Orr', DATE '2001-04-06', 70000,1 FROM DUAL UNION ALL
SELECT 5, 'Vicky', 'Palazzo', DATE '2001-04-07', 88000,2 FROM DUAL UNION ALL
SELECT 6, 'Cheryl', 'Ford', DATE '2001-04-08', 110000,1 FROM DUAL UNION ALL
SELECT 7, 'Leslee', 'Altman', DATE '2001-04-10', 66666, 1 FROM DUAL UNION ALL
SELECT 8, 'Jill', 'Coralnick', DATE '2001-04-11', 190000, 2 FROM DUAL UNION ALL
SELECT 9, 'Faith', 'Aaron', DATE '2001-04-17', 122000,2 FROM DUAL;
9 rows affected

select 
     d.department_id,
     d.department_name
from departments d left join employees e 
on e.department_id=d.department_id
where e.employee_id is null


DEPARTMENT_ID
DEPARTMENT_NAME


3
Sales


select department_id, department_name
from departments
where department_id not in (select department_id from employees)


DEPARTMENT_ID
DEPARTMENT_NAME


3
Sales


select department_id, department_name
from departments
minus
select 
     d.department_id,
     d.department_name
from departments d join employees e 
on e.department_id=d.department_id


DEPARTMENT_ID
DEPARTMENT_NAME


3
Sales