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1. Introduction

# The Basic Mathematics of SQL

## Introduction

Formally, we know a relation is a subset of a Cartesian Products of sets. i.e $R \in ( A X B )$
For Example.
$$A = \{ 1, 3 \} , B = \{ 2, 5 \}$$
Cartesian Product of set A and B will be
$$P = \{ (1,2),(3,2),(1,5),(3,5)\}$$

Out of that there are three pair that observe the $<$ relationship
$$R = \{ (1,2), (1,5), (3,5)\}$$
Or we can 1 is related to 5 by relation R ($<$)

In real world we name each relation by name which makes sense for others,
and with each relation name we associate its schema - which is a sequence of
attributes(i.e a column in Table)

For Example for above set we have a relation of $R (A,B)$ which we can write more as

• lessthan(A,B)
In Real world we represent the relation in Table with attributes as column
• Student(Id, FirstN, LastN)
ID FirstN LastN
101 John Deo
102 Jane Deo
103 Jhonny Deo

Note : Attributes names in relation schema must be different