relational

Question 1

What is relational algebra?

Answer 1

A procedural query language for relational databases

Relational algebra provides a formal foundation for querying and manipulating data in a relational database.

Question 2

Which of the following is NOT a fundamental operation in relational algebra?

Answer 2

INSERT

Fundamental operations include SELECT, PROJECT, and JOIN.

Question 3

What does the SELECT operation do in relational algebra?

Answer 3

Chooses specific rows

The SELECT operation filters rows based on a specified condition.

Question 4

What does the PROJECT operation do?

Answer 4

Selects specific columns from a table

The PROJECT operation is used to retrieve specific attributes from a relation.

Question 5

Which symbol represents the UNION operation in relational algebra?

Answer 5

∪

The UNION operation combines the results of two relations, removing duplicates.

Question 6

Which type of JOIN returns all rows from both relations?

Answer 6

FULL OUTER JOIN

A FULL OUTER JOIN includes all records from both tables, matching where possible.

Question 7

What is the purpose of the RENAME operation?

Answer 7

To change the name of a relation

The RENAME operation allows for the aliasing of relations for clarity in queries.

Question 8

What does the INTERSECT operation do?

Answer 8

Returns rows that are in both relations

The INTERSECT operation yields the common rows from two relations.

Question 9

In relational calculus, what does the term ‘tuple’ refer to?

Answer 9

A single row in a relation

A tuple represents a single entry in a table, corresponding to a record.

Question 10

What does the term ‘domain’ refer to in relational calculus?

Answer 10

The set of all possible values for an attribute

The domain defines the permissible values that an attribute can take.

Question 11

Which of the following symbols represents the existential quantifier in relational calculus?

Answer 11

∃

The existential quantifier indicates that there exists at least one tuple satisfying a condition.

Question 12

What is the purpose of the universal quantifier in relational calculus?

Answer 12

To specify that a condition holds for all tuples

The universal quantifier is used to express conditions that must be true for every tuple in a relation.

Question 13

In tuple relational calculus, how is a query expressed?

Answer 13

Using logical predicates

Queries in tuple relational calculus are formulated with logical conditions rather than procedural steps.

Question 14

Which operation can be used to combine two relations with the same attributes?

Answer 14

UNION

The UNION operation merges two relations, eliminating duplicates.

Question 15

What is the result of a CROSS JOIN?

Answer 15

A combination of rows from two relations without conditions

A CROSS JOIN produces a Cartesian product of the two relations.

Question 16

Which of the following statements about relational calculus is true?

Answer 16

It is a declarative language.

Relational calculus specifies what to retrieve rather than how to retrieve it.

Question 17

What is the main advantage of relational algebra?

Answer 17

It provides a clear procedural approach to queries

Relational algebra gives a structured way to express queries through defined operations.

Question 18

In relational algebra, what does the term ‘set difference’ refer to?

Answer 18

The result of removing common rows from two relations

Set difference yields rows that are in one relation but not in another.

Question 19

What type of queries can relational calculus express?

Answer 19

Complex queries involving multiple relations

Relational calculus supports intricate queries that may involve several relations and conditions.

Question 20

Which of the following is a valid tuple relational calculus expression?

Answer 20

{t | t ∈ Student ∧ t.Age > 20}

This expression selects tuples from the Student relation where the Age attribute is greater than 20.

Question 21

What does the term ‘result set’ refer to in the context of relational algebra?

Answer 21

The final output of a query

The result set is what is returned after the execution of a query.

Question 22

Which of the following is NOT a characteristic of relational algebra?

Answer 22

It is non-procedural.

Relational algebra is procedural, specifying the steps to retrieve data.

Question 23

What is the main purpose of using the aggregate functions in relational algebra?

Answer 23

To perform calculations on a set of values

Aggregate functions like SUM, COUNT, and AVG summarize data.

Question 24

What is the significance of the ORDER BY clause in SQL?

Answer 24

To sort the output of a query

The ORDER BY clause organizes the results based on specified columns.

Question 25

Which of the following is an example of an aggregate function?

Answer 25

All of the above ## Footnote COUNT(), SUM(), and AVG() are all aggregate functions used to calculate values from a set.

Question 26

In relational calculus, which of the following is true about the variables used?

Answer 26

They can represent tuples from a relation ## Footnote Variables in relational calculus can be used to denote any tuple from a specified relation.

Question 27

What is the difference between a LEFT JOIN and a RIGHT JOIN?

Answer 27

LEFT JOIN returns all rows from the left table and matched rows from the right ## Footnote A RIGHT JOIN does the opposite, returning all rows from the right table.

Question 28

Which operation is used to count the number of tuples in a relation?

Answer 28

COUNT ## Footnote The COUNT operation returns the total number of rows in a relation.

Question 29

What is a primary key?

Answer 29

A unique identifier for a table ## Footnote A primary key ensures that each record in a table can be uniquely identified.

Question 30

What is the main advantage of using relational algebra?

Answer 30

It provides a clear procedural approach to queries ## Footnote This clarity aids in understanding how data is retrieved and manipulated.

Question 31

What is the purpose of the GROUP BY clause in SQL?

Answer 31

To group rows that have the same values in specified columns ## Footnote The GROUP BY clause is often used with aggregate functions to summarize data.

Question 32

Which of the following is a property of the UNION operation?

Answer 32

It requires the same number of attributes in both relations ## Footnote The UNION operation can only combine relations with the same number and types of attributes.

Question 33

What is the significance of using the DISTINCT keyword in SQL?

Answer 33

It removes duplicate rows from the result set ## Footnote The DISTINCT keyword ensures that each row in the output is unique.

Question 34

In relational algebra, what does the term 'join' refer to?

Answer 34

Combining two relations based on a common attribute ## Footnote Joins are essential for retrieving data from multiple related tables.

Question 35

What is a foreign key?

Answer 35

A primary key that references another table ## Footnote Foreign keys establish relationships between tables by linking records.

Question 36

What does a natural join do?

Answer 36

Combines two relations based on a common attribute ## Footnote A natural join automatically matches columns with the same name in both tables.