Question 1

Although correlated subqueries are useful in database redesign,they cannot be used to verify functional dependencies.

Accepted Answer

Correlated subqueries can indeed be used to verify functional dependencies by checking if a particular column or set of columns determines another column's value, thus ensuring data integrity and normalization in database design.

Question 2

A doubly nested set of NOT EXISTS SELECT statements can be used to find rows that meet some specified condition for every row in a table.

Accepted Answer

A doubly nested set of NOT EXISTS SELECT statements can be used to perform a correlated subquery, which checks for a condition in every row of the outer query result set.

Question 3

In a correlated subquery,the same table is used in the upper and lower SELECT statements.

Accepted Answer

In a correlated subquery, the inner or lower SELECT statement references a column from the outer or upper SELECT statement, which is usually the same table.

Question 4

Database redesign is rarely needed because databases are usually built correctly the first time.

Accepted Answer

Database redesign is often necessary due to changes in business requirements, technology updates, or changes in data structures, making it unlikely that a database would be built perfectly the first time.

Question 5

The use of a doubly nested set of NOT EXISTS SELECT statements is a famous pattern in SQL use.

Accepted Answer

The use of a doubly nested set of NOT EXISTS SELECT statements is a well-known pattern in SQL use.

Question 6

Correlated subqueries can be used to verify functional dependencies.

Accepted Answer

Correlated subqueries can be used to verify whether a certain value exists in a related table or to filter a result set based on a condition in a related table. However, they are not generally used to verify functional dependencies.

Question 7

In the SQL statement:
SELECT S1.CustName,S1.SalesRepNo FROM SALES S1;
the "S1" is called an alias.

Accepted Answer

"S1" is used to give a shorter, alternative name for the table "SALES" so that it can be referred to more easily in the SELECT statement. This is called an alias.

Question 8

EXISTS and NOT EXISTS are actually just another form of correlated subqueries.

Accepted Answer

EXISTS and NOT EXISTS are subqueries that are correlated with the outer query, meaning they reference columns from the outer query in order to determine if a row should be included in the result set. Therefore, they are considered to be a type of correlated subquery.

Question 9

In a correlated subquery,the DBMS can run the lower SELECT statement by itself and then send the results to the upper SELECT statement.

Accepted Answer

In a correlated subquery, the inner query depends on the outer query for its values, meaning it cannot be executed independently without the context provided by the outer query.

Question 10

In the database redesign process,two SQL tools are useful for testing whether or not certain conditions or assumptions are valid: uncorrelated subqueries and EXISTS/NOT EXISTS.

Accepted Answer

The answer of In the database redesign process,two SQL tools...

Question 11

There is a common trap in writing a correlated subquery,which will cause no rows to ever be displayed in the results.

Accepted Answer

This is true. The trap occurs when the subquery is not properly correlated to the main query, causing the subquery to always return null or no rows, resulting in no output from the main query.

Question 12

Database redesign is equally difficult whether or not the database has data in it.

Accepted Answer

Redesigning a database that already contains data is generally more difficult because it requires careful migration of the existing data, ensuring data integrity and compatibility with the new design, which can be complex and time-consuming.

Question 13

In a correlated subquery,the DBMS must run the lower SELECT statement as a process that is nested within the upper SELECT statement.

Accepted Answer

In a correlated subquery, the lower SELECT statement depends on the results of the outer SELECT statement, so it must be executed for each row returned by the outer query. This nesting behavior is what makes the subquery "correlated" to the outer query.

Question 14

In a real sense,information systems and organizations do not just influence each other,but rather they create each other.

Accepted Answer

Information systems and organizations are intertwined and constantly co-create each other. Organizations shape and influence the development and use of information systems, and in turn, information systems shape and influence the practices and structure of organizations. The two are highly interdependent and constantly evolving together.

Question 15

A continuous circular process of changes in user behaviors and change in the information systems they use is a natural outcome of information system use.

Accepted Answer

As users interact with information systems, their behaviors and expectations change. In response, information systems are modified or replaced with new technologies, leading to a continuous circular process of change.

Question 16

When using queries with EXISTS and NOT EXISTS,the processing of the associated SELECT statements must be nested.

Accepted Answer

When using EXISTS and NOT EXISTS, the processing of the associated SELECT statements must be nested within the main query. This means that the subquery (SELECT statement) is executed for each row of the main query.

Question 17

Because EXISTS and NOT EXISTS are forms of correlated subqueries,the processing of the associated SELECT statements must be nested.

Accepted Answer

EXISTS and NOT EXISTS subqueries are correlated subqueries and their processing involves nesting the associated SELECT statements. This is because the subquery references columns from the outer query, and the database engine must evaluate the subquery for each row of the outer query.

Question 18

In the database redesign process,it is often useful to test whether certain conditions or assumptions are valid before proceeding with the redesign.

Accepted Answer

It is important to test assumptions and conditions before proceeding with a database redesign in order to avoid costly errors or inefficiencies. By conducting tests or experiments, designers can verify that their proposed changes will work as intended and identify any potential issues or challenges that may arise. This can help to minimize risks and ensure that the resulting database is reliable, efficient, and effective.

Question 19

A correlated subquery looks very different from a noncorrelated subquery.

Accepted Answer

A correlated subquery is distinguished from a noncorrelated subquery not by its appearance but by its operation. Both can look similar syntactically, but a correlated subquery depends on values from the outer query for its execution, while a noncorrelated subquery can run independently.

Question 20

The continuous circular process of changes is known as the Systems Development Life Cycle (SDLC).

Accepted Answer

The Systems Development Life Cycle (SDLC) is a continuous process of planning, designing, coding, testing, and maintaining a system or software application. It is a circular process because once the application is developed and deployed, it needs to be updated and maintained to adapt to changing user needs and technology advancements.

Quiz 8: Database Redesign