What about the least number?
select count(*) from member as t1 join party as t2 on t1.party_id = t2.party_id group by t1.party_id order by count(*) asc limit 1
How about the max?
select count(*) from member as t1 join party as t2 on t1.party_id = t2.party_id group by t1.party_id order by count(*) desc limit 1
What is the name of the party that has this number per party?
select t2.party_name from member as t1 join party as t2 on t1.party_id = t2.party_id group by t1.party_id order by count(*) desc limit 1