CREATE TABLE ENROLLED_IN (Grade VARCHAR(255), StuID VARCHAR(255)); CREATE TABLE STUDENT (LName VARCHAR(255), StuID VARCHAR(255)); CREATE TABLE GRADECONVERSION (gradepoint INTEGER, lettergrade VARCHAR(255))
Find the average grade point of student whose last name is Smith.
    
SQL: 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"