Which architects have built bridges?
select distinct t1.name from architect as t1 join bridge as t2 on t1.id = t2.architect_id
Which of them have built bridges longer than 80 meters?
select distinct t1.name from architect as t1 join bridge as t2 on t1.id = t2.architect_id where t2.length_meters > 80
How many of those architects have also built mills?
select count(distinct t2.name) from mill as t1 join architect as t2 on t1.architect_id = t2.id join bridge as t3 on t3.architect_id = t2.id where t3.length_meters > 80
Please list the names of those mills.
select distinct t1.name from mill as t1 join architect as t2 on t1.architect_id = t2.id join bridge as t3 on t3.architect_id = t2.id where t3.length_meters > 80