How many projects are there?
select count ( project_id ) from project_staff
How many staff are there?
select count ( staff_id ) from project_staff
What project has the most staff?
select project_id from project_staff group by project_id order by count ( staff_id ) desc limit 1
Which staff started the earliest?
select staff_id from project_staff order by date_from limit 1
Yes.
select date_from from project_staff where staff_id = 56.0