Intro to Relational Algebra

Question 1

Structured Query Language

Answer 1

SQL: application-level query language, declarative

Question 2

Relational algebra

Answer 2

used to represent queries internally, intermediate language used within DBMS

Question 3

RA queries

Answer 3

relations are treated as sets, no dupilcates allowed, result is always a relation

Question 4

Unary operation

Answer 4

OP [R] => new relation

Question 5

Binary operation

Answer 5

[R] Op [S] => new relation

Question 6

Operator precedence

Answer 6

Selection
Projection
Cartesian product
Join
Set operations
Parentheses

Question 7

Selection (σ)

Answer 7

filter rows based on a condition

Question 8

Projection (π)

Answer 8

select specific columns, no duplicate attributes

Question 9

Cartesian product (×)

Answer 9

combine all rows from two relations (E)

Question 10

Join (⋈)

Answer 10

join relations to form longer tuples (NE). AKA inner join

Question 11

Theta Join

Answer 11

general condition with any comparison operator

Question 12

Equijoin

Answer 12

equality condition on one or more specified attributes

Question 13

Natural Join

Answer 13

equality condition on all common attributes

Question 14

Outer Join variations

Answer 14

Left outer join [left + middle]
Right outer join [middle + right]
Full outer join [left + middle + right]

Question 15

Set operations

Answer 15

Union, intersection, difference

Question 16

SQL temporary tables

Answer 16

allows virtual representation derived from base relations