Midterms - Relational algebra

Question 1

Identification

Fundamental operations to retrieve and manipulate tuples in a relation

Answer 1

Relational Algebra

Question 2

Identification

Generate a relation with tuples that contains only speciefied attributes

• Can rearrange order of attributes
• Can manipulate values

Answer 2

Projection

Question 3

Identification

Choose a subset of the tuples from a relation that satisfies a selection predicate

Answer 3

Select

Question 4

Identification

acts as a filter to retain only tuples that fulfill its qualifying requirement

Answer 4

Predicate

Question 5

Identification

Can combine multiple predicates using conjuctions/disjunctions

Answer 5

Select

Question 6

Identification

Generate relation that contains only the tuples that appear in both of the input relations

Answer 6

Intersection

Question 7

Identification

Generate a relation that contains all tuples that appear in either only one or both input relations

Answer 7

Union

Question 8

Identification

Generate a relation that contains only the tuples that appear in the first and not the second of the input relations

Answer 8

Difference

Question 9

Identification

Generate a relation that contains all tuples that are a combination of two tuples with common values for one or more attributes

Answer 9

Join

Question 10

Identification

Generate a relation that contains all possible combinations of tuples from the input relations

Answer 10

Product

Question 11

Relational Algebra: Syntax

Product

Answer 11

R × S

SELECT * FROM R CROSS JOIN S;

Question 12

Relational Algebra: Syntax

Join

Answer 12

R ⋈ S

SELECT * FROM R NATURAL JOIN S;

Question 13

Relational Algebra: Syntax

Difference

Answer 13

R - S

(SELECT * FROM R)
EXCEPT
(SELECT * FROM S);

Except operation is not supported in mysql, use alternative: Not in ()

Question 14

Relational Algebra: Syntax

Union

Answer 14

R ∪ S

(SELECT * FROM R)
UNION ALL 
(SELECT * FROM S);

Question 15

Relational Algebra: Syntax

Intersection

Answer 15

R ∩ S

(SELECT * FROM R)
INTERSECT
(SELECT * FROM S);

Intersect is not supported in mysql, use alternative: Inner Join

Question 16

Relational Algebra: Syntax

Select

Answer 16

σcondition(relation)

Select * from R WHERE a_id = 'a2' AND b_id > 102

Question 17

Relational Algebra: Syntax

Projection

Answer 17

π attribute1, attribute2, …(relation)

Select b_id-100, a_id FROM R WHERE a_id = 'a2'