What are the names of reviewers who had rated 3 star and 4 star?
SELECT T2.name FROM Rating AS T1 JOIN Reviewer AS T2 ON T1.rID  =  T2.rID WHERE T1.stars  =  3 INTERSECT SELECT T2.name FROM Rating AS T1 JOIN Reviewer AS T2 ON T1.rID  =  T2.rID WHERE T1.stars  =  4
reviewers who had rated 3 and 4 stars refers to filtering conditions WHERE T1.stars = 3 AND WHERE T1.stars = 4; names of reviewers refers to T2.name; using INTERSECT to find common reviewers between two conditions; joining tables Rating and Reviewer to relate ratings to reviewers.