Page 456 - Computer_Science_F5

and Alternate keys) in a relational (b) Foreign key: An attribute that
database by examining the student
registration and results tables in your
school.
FOR ONLINE READING ONLY
Materials:
Database Management System
(DBMS) Software (Such as MySQL,
PostgreSQL, or SQLite ); Access
to Student registration and results
tables from your school’s database
or a sample dataset provided for the
activity; Diagramming Tool (such as
Lucidchart, Draw.io, or even a pen and
paper to create visual representations
of the tables and their relationships);
Sample Data or Dataset (gather or
simulate sample data for student
registration and results tables).
Instructions:
Consider the related tables of student
registration and results in your school.
Identify and illustrate them with a
diagram.
Step 1: Examine the tables
(a) Student registration table: This
table contains information about
the students.
(b) Student results table: This table
contains information about the
students’ results.
Step 2: Identify the Keys
(a) Primary key: The unique identifier
for each row in a table.
447
Student’s Book Form Five
Computer Science Form 5.indd 447
creates a relationship between two
tables.
(c) Candidate key: A set of attributes
that can uniquely identify a row in Chapter Eight: Databases and Database Management Systems
a table.
(d) Alternate key: Candidate keys that
are not chosen as the primary key.
Step 3: Illustrate the Keys using
diagram
(a) Draw a diagram to show the
relationship between the Student
Registration and Student Results
tables.
(b) Indicate the Primary, Foreign,
Candidate, and Alternate keys.
Deliverables:
Write a brief report on the relational
database keys identified from your
school databases, including the
screenshots. Document your findings
in a portfolio.
Selection and projection
Selection and projection operations are
basic and most used operations specific
to relational databases. The selection is
defined as taking the horizontal subset
of rows of a single table that satisfies a
particular condition. It retrieves tuples
from a relation, limiting the results to
only those that meet a specific criterion.
Selection answers the question: which
rows shall the query return (where
condition)? For example, `Select *
From emp Where deptno = 10` as
shown in Figure 8.11.
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