Select records in Mysql if the other column is set to none

how can I get all the departments where is a ID is equal to manager column or if the manager is set to NULL it is equal to the supervisor.

table_department:

dept_id, dept_name, manager_id, supervisor_id

1     IT-admin           1            NULL
2     IT-hardware       NULL           1
3     IT-system          4             1
4     Engineering        3            NULL

table_users:

user_id, username 
1       username1
2       username2
3       username3
4       username4
5       username5

If in my condition the user is username1 and his id is 1, How to query and show IT-admin and IT-hardware department because username1 is the manager/supervisor of that departments.

Any help would be appreciated, Thank you.

>Solution :

Try this:

SELECT dept_id, dept_name, user_id, username
FROM table_department 
INNER JOIN table_user ON COALESCE(manager_id, supervisor_id) = user_id;