SELECT project_details FROM Projects WHERE project_id NOT IN ( SELECT project_id FROM Project_Staff WHERE role_code  =  'researcher' )
List the project details of the projects which did not hire any staff for a researcher role.
SELECT project_details FROM Projects WHERE project_id NOT IN ( SELECT project_id FROM Project_Staff WHERE role_code = 'researcher ' )
select project_details from projects where project_id not in ( select project_id from project_staff where role_code = value )
List the project details of the projects which did not hire any staff for a researcher role .