Testing SQL queries: To test if a query specified in English has been correctly written in SQL, the SQL query is typically executed on multiple test databases, and a human checks if the SQL query result on each test database matches the intention of the specification in English.a. In Section 4.1.1 we saw an example of an erroneous SQL query which was intended to find which courses had been taught by each instructor; the query computed the natural join of instructor, teaches, and course, and as a result it unintentionally equated the dept name attribute of instructor and course. Give an example of a dataset that would help catch this particular error.b. When creating test databases, it is important to create tuples in referenced relations that do not have any matching tuple in the referencing relation for each foreign key. Explain why, using an example query on the university database.c. When creating test databases, it is important to create tuples with nullvalues for foreign-key attributes, provided the attribute is nullable (SQLallows foreign-key attributes to take on null values, as long as they are not part of the primary key and have not been declared as not null). Explain why, using an example query on the university database.

Computer Networking: A Top-Down Approach (7th Edition)

7th Edition

ISBN:9780133594140

Author:James Kurose, Keith Ross

Publisher:James Kurose, Keith Ross

Chapter1: Computer Networks And The Internet

Section: Chapter Questions

Problem R1RQ: What is the difference between a host and an end system? List several different types of end...

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Testing SQL queries: To test if a query specified in English has been correctly written in SQL, the SQL query is typically executed on multiple test databases, and a human checks if the SQL query result on each test database matches the intention of the specification in English.
a. In Section 4.1.1 we saw an example of an erroneous SQL query which was intended to find which courses had been taught by each instructor; the query computed the natural join of instructor, teaches, and course, and as a result it unintentionally equated the dept name attribute of instructor and course. Give an example of a dataset that would help catch this particular error.
b. When creating test databases, it is important to create tuples in referenced relations that do not have any matching tuple in the referencing relation for each foreign key. Explain why, using an example query on the university database.
c. When creating test databases, it is important to create tuples with null
values for foreign-key attributes, provided the attribute is nullable (SQL
allows foreign-key attributes to take on null values, as long as they are not part of the primary key and have not been declared as not null). Explain why, using an example query on the university database.

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