CREATE TABLE ENROLLED_IN (Grade VARCHAR2, StuID VARCHAR2)
CREATE TABLE STUDENT (LName VARCHAR2, StuID VARCHAR2)
CREATE TABLE GRADECONVERSION (gradepoint NUMBER, lettergrade VARCHAR2)

Find the average grade point of student whose last name is Smith.
SELECT AVG(T2.gradepoint) FROM ENROLLED_IN AS T1 JOIN GRADECONVERSION AS T2 JOIN STUDENT AS T3 ON T1.Grade = T2.lettergrade AND T1.StuID = T3.StuID WHERE T3.LName = "Smith"
SELECT AVG("T2"."gradepoint") FROM "ENROLLED_IN" "T1" JOIN "GRADECONVERSION" "T2" ON "T1"."Grade" = "T2"."lettergrade" JOIN "STUDENT" "T3" ON "Smith" = "T3"."LName" AND "T1"."StuID" = "T3"."StuID"