How many mills did each architect build?
select t1.name, count(*) from architect as t1 join mill as t2 on t1.id = t2.architect_id group by t1.id order by count(*)
Order by decreasing number of mills built.
select t1.name, count(*) from architect as t1 join mill as t2 on t1.id = t2.architect_id group by t1.id order by count(*) desc
Which architect built the most mills?
select t1.name from architect as t1 join mill as t2 on t1.id = t2.architect_id group by t1.id order by count(*) desc limit 1
Please list his id and nationality as well.
select t1.id, t1.name, t1.nationality from architect as t1 join mill as t2 on t1.id = t2.architect_id group by t1.id order by count(*) desc limit 1