List the names of architects who built 2 bridges.
select t1.name from architect as t1 join bridge as t2 on t1.id = t2.architect_id group by t1.id having count(*) = 2
Include architects who built 1 mill.
select t1.name from architect as t1 join bridge as t2 on t1.id = t2.architect_id group by t1.id having count(*) = 2 union select t1.name from architect as t1 join mill as t2 on t1.id = t2.architect_id group by t1.id having count(*) = 1
Include their ids and genders as well.
select t1.id, t1.name, t1.gender from architect as t1 join bridge as t2 on t1.id = t2.architect_id group by t1.id having count(*) = 2 union select t1.id, t1.name, t1.gender from architect as t1 join mill as t2 on t1.id = t2.architect_id group by t1.id having count(*) = 1