Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE Project_Staff ( date_from VARCHAR, date_to VARCHAR, project_id VARCHAR, role_code VARCHAR )

### Question ###
List from which date and to which date these staff work: project staff of the project which hires the most staffs

### Accurate SQL ###

SELECT date_from, date_to FROM Project_Staff WHERE project_id IN (SELECT project_id FROM Project_Staff GROUP BY project_id ORDER BY COUNT(*) DESC LIMIT 1) UNION SELECT date_from, date_to FROM Project_Staff WHERE role_code = 'leader'