Relational Languages

Question 1

what is relational algebra

Answer 1

a procedural query language

Question 2

what is the difference between SQL and relational algebra

Answer 2

RA recursively performs operations on a relation to form a new relation

Question 3

what are the unary relational operations (3)

Answer 3

select σ

project Π

rename ρ

Question 4

give the relational algebra from set theory (3)

Answer 4

union U
Elements of both A and B

set difference -
Elements of A not in B

cartesian product X
product of the sets of records from two or more joined tables

Question 5

what are the binary operations (4)

Answer 5

theta join R ⋈_θ S

equi join R ⋈_= S

natural join R ⋈ S

outer joins
R ⟕ S left
R ⟖ S right
R ⟗ S full outer join