Left Outer Join course natural left outer join prereg course id title dept name credits prereq id BIO-301 Genetics Biology 4 BIO-101 CS-190 Game Design Comp.Sci. 4 CS-101 CS-315 Robotics Comp.Sci. 3 null Database System Concepts-6th Edition 4.6 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 6 4.6 ©Silberschatz, Korth and Sudarshan th Edition Left Outer Join course natural left outer join prereq