List the project details of the projects which did not hire any staff for a researcher role.
create table projects (project_details varchar, project_id varchar, role_code varchar, PRIMARY KEY (project_details)); create table project_staff (project_details varchar, project_id varchar, role_code varchar, PRIMARY KEY (project_details))
select project_details from projects where not project_id in (select project_id from project_staff where role_code = 'researcher')