CREATE TABLE TRACK (UnitPrice NUMBER, GenreId VARCHAR2)
CREATE TABLE GENRE (GenreId VARCHAR2, Name VARCHAR2)

What is the average unit price of rock tracks?
SELECT AVG(T2.UnitPrice) FROM GENRE AS T1 JOIN TRACK AS T2 ON T1.GenreId = T2.GenreId WHERE T1.Name = "Rock"
SELECT AVG("T2"."UnitPrice") FROM "GENRE" "T1" JOIN "TRACK" "T2" ON "T1"."GenreId" = "T2"."GenreId" WHERE "Rock" = "T1"."Name"