Question

For this week let’s discuss the concepts of primary keys and table indexes.

• What types of data might serve as a valuable index for a table?
• What types of data would be unsuitable as a primary key?

Give some examples of data types and fields that you might use for certain scenarios and also what types are not good to use.

Answer 1

# To discuss these concepts we suppose primay key as a mapping concept  and index value as array concept.

# So from here you may start thinking about what is array.

# Array-> Is a collection of similar data type , which is used for storage purpose of similar data .

Suppose you have U.S Dollars of different prices from 0-10. (similar data type)

  you wanted to count them how many u have for a particular coin.

for that purpose you can use array

Amount counting

$ 0 -> 0

$ 1 -> 2   

$ 2 -> 3

$ 3 -> 4

$ 4 -> 7

$ 5 -> 8

$ 6 -> 9

$ 7 -> 4   

$ 8 -> 6

$ 9 -> 8

$ 10 -> 2

  

ARRAY

0

2

3

4

7

8

9

4

6

8

2

Index 0 1 2 3 4 5 6 7 8 9 10

Here index work -> coin number.(similar data type)

c++/c++14

#include<iostream>

using namespace std;

int main()

{

int a[11]; // this way you can intilise an array.

for (int i=0;i<11;++i) // loop for iteration

{

cin>>a[i];

}

}

# MAPPING-> suppose we have two array's and after combining both of them we get mapping

KEY POINTS:

1. Primary key -> Is unique , it can't be similar.

2. value of key -> It can be similar or different

Suppose Goku , Ash , Friza and Naruto are friends all of them have different U.S doller ammount

Name Amount

Goku -> $ 450

Ash -> $ 1200

Friza -> $ 900

Naruto -> $ 450

Method->1

we can use two array to store both values

Array-1 store Names

Goku

Ash

Friza

Naruto

Index 0   1 2 3

Array-2 store Amount they have

450

1200

900

450

Index 0   1 2 3

  Method->2

use a single map

primary key	value of key
Ash	1200
Friza	900
Goku	450
Naruto	450

Note->mapping has the property to sort accordingly to it's primay key.

use->you can write names and they will come in sorted (Dictionary manner).

program in mapping

Note-> map header file in mendotary

#include<iostream>

#inlcude<map>

using namespace std;

int main()

{

map<string,int> a; // this way you can declare map.

for (int i=0;i<4;++i) // loop for iteration

{

string s;

int amount ;

cout<<"\n Enter name: ";

cin>>s;  

cout<<"Enter amount they have: ";

cin>>amount;

}

}

Disanvantage of using map -> It use more memory as compare to array, that's why use map only in case of storing related data in case of non-relative data use array.