How many mills are built by American architects?
select count ( * ) from mill as t1 join architect as t2 on t1.architect_id = t2.id where t2.nationality = 'American'
Hmm, I also want to know how many mills are built by Canadian architects.
select count ( * ) from mill as t1 join architect as t2 on t1.architect_id = t2.id where t2.nationality = 'Canadian'
What are the distinct type of mills that are built by American or Canadian architects?
select distinct t1.type from mill as t1 join architect as t2 on t1.architect_id = t2.id where t2.nationality = 'American' or t2.nationality = 'Canadian'