Computer Science: An Overview: Global Edition (12th Edition)

Published by Pearson Higher Education
ISBN 10: 1292061162
ISBN 13: 978-1-29206-116-0

Chapter 9 - Database Systems - Section 9.2 - The Relational Model - Questions & Exercises - Page 431: 2

Answer

One solution is $$ \begin{array}{l}{\text { TEMP } \leftarrow \text { SELECT from JOB }} \\ {\text { where Dept = "PERSONNEL" }} \\ {\text { LIST } \leftarrow \text { PROJECT JobTitle from TEMP }}\end{array} $$ In some systems, this results in a list with a job title repeated, depending on how many times it occurred in the personnel department. That is, our list might contain numerous occurrences of the title secretary. It is more common, however, to design the PROJECT operation so that it removes duplicate tuples from the resulting relation.

Work Step by Step

One solution is $$ \begin{array}{l}{\text { TEMP } \leftarrow \text { SELECT from JOB }} \\ {\text { where Dept = "PERSONNEL" }} \\ {\text { LIST } \leftarrow \text { PROJECT JobTitle from TEMP }}\end{array} $$ In some systems, this results in a list with a job title repeated, depending on how many times it occurred in the personnel department. That is, our list might contain numerous occurrences of the title secretary. It is more common, however, to design the PROJECT operation so that it removes duplicate tuples from the resulting relation.
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