CREATE TABLE Projects (project_details VARCHAR(255), project_id VARCHAR(255), role_code VARCHAR(255)); CREATE TABLE Project_Staff (project_details VARCHAR(255), project_id VARCHAR(255), role_code VARCHAR(255))
List the project details of the projects which did not hire any staff for a researcher role.
    
SQL: SELECT project_details FROM Projects WHERE NOT project_id IN (SELECT project_id FROM Project_Staff WHERE role_code = 'researcher')