Flashcards in Relational Algebra Deck (21):

1

## Unary Relational Operations

###
Operations on one set:

Select: sigma: σ

Project: pi: π

Rename: rho: ρ

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## Select: σ

### Selects entire entries from a table

3

## Project: π

### Selects only specified attributes

4

## Rename: ρ

### Renames attributes or entities

5

## Binary Operations:

###
Operations on two sets:

Union: U

Intersection: ∩

Set Difference: -

6

## Union

### Includes all tuples from R and S, or R, or S

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## Intersection

### Includes all tuples in R and S

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## Set Difference:

### Includes all the tuples in R but not S (R-S)

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## Commutative Operatiosn

### Union and Intersection

10

## Joins:

###
Binary Operators:

Cross Product: X

Theta: Θ

Equi-join Θ=

Natural Join: *

11

## Cartesian Product / Cross Product

### Exhausting pairing

12

## Theta Join

### A join based on any sort of equality, can be combined with ANDs

13

## Equijoin

### A join based on only strict equality pairing

14

## Natural Join

### Removes superfluous attributes in an equijoin situation

15

## Outer Joins

### Keeps tuples in R even if they aren't in S

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## Left Outer Join

### Keep every tuple in the left relation, pad with nulls

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## Right Outer Join

### Keep every tuple in the right relation, pad with nulls

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## Full Outer Join

### Keeps every tuple in right and left relation regardless of matches, pad with nulls

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## Aggregate Functions

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F(Max)

F(Min)

F(Sum)

F(Count)

F(Average)

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## Grouping with Aggregate Functions

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Given a relation: EMP(EMPNO, DNO, SAL)

DNO F(AVERAGE)SAL(EMP)

Groups by the DNO

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