How many projects are there?
select count ( * ) from projects
How many of those projects did not hire anyone for a researcher role?
select count ( project_id ) from projects where project_id not in ( select project_id from project_staff where role_code = 'researcher' )
What are the details of those projects?
select project_details from projects where project_id not in ( select project_id from project_staff where role_code = 'researcher' )