CREATE TABLE ENROLLED_IN (Grade VARCHAR, StuID VARCHAR)
CREATE TABLE STUDENT (LName VARCHAR, StuID VARCHAR)
CREATE TABLE GRADECONVERSION (gradepoint INT, lettergrade VARCHAR)

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" AS "T1" JOIN "GRADECONVERSION" AS "T2" ON "T1"."Grade" = "T2"."lettergrade" JOIN "STUDENT" AS "T3" ON "Smith" = "T3"."LName" AND "T1"."StuID" = "T3"."StuID"