What you wrote is the same as:
FROM departments d
join employees e
ON d.manager_id = e.manager_id
AND d.department_id = e.department_id
The tables share two similarly named column so the natural join will link them both (i.e.: MANAGER_ID and DEPARTMENT_ID).
Try this instead:
join employees USING ( department_id )
Thank you very much it has worked.
I am very new to sql....