Show me the names of all the reviewers.
select name from reviewer
What about the ratings they have contributed?
select * from rating as t1 join reviewer as t2 on t1.rid = t2.rid
Show me the reviewers who have contributed three or more ratings.
select t2.name from rating as t1 join reviewer as t2 on t1.rid = t2.rid group by t1.rid having count(*) >= 3