Suppose we have three relations r(A, B), s(B, C), and t(B, D), with all attributes declared as not null. Consider the expressions • r natural left outer join (s natural left outer join t), and • ( natural left outer join s) natural left outer join t a. Give instances of relations r, s and t such that in the result of the second expression, attribute C has a null value but attribute D has a non-null value. b. Is the above pattern, with C null and D not null possible in the result of the first expression? Explain why or why not.

Suppose we have three relations r(A, B), s(B, C), and t(B, D), with all attributes declared as not null. Consider the expressions • r natural left outer join (s natural left outer join t), and • ( natural left outer join s) natural left outer join t a. Give instances of relations r, s and t such that in the result of the second expression, attribute C has a null value but attribute D has a non-null value. b. Is the above pattern, with C null and D not null possible in the result of the first expression? Explain why or why not.

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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