1.  It was originally proposed to separate the physical storage of data from its conceptual representation and to provide a mathematical foundation for data representation and querying, 
it is very common database that helps storing data into tables, many companies have made this their reliable way of putting tables together. 

2. SQL is an abbreviation for Structured Query Language, and a query language's job is mostly to collect specific data of databases, which makes SQL is unique langauge that is used to 
communicate with the database.

3. ER stands for Entity Relationship, which is a type of flowchart that compares the subjects all together to see whether there is any related concepts within the database.

4. one-to-one: this is a type of relationship that indicates that for one input there is one specific output to it, and so on and so forth. 
   one-to-many: this type of relationship indicates that one input can have many different outputs, opposite of one-to-one. 
   many-many: this type of relationship indicates whether A and B could contain parent instances, where either of them have many children in the dateset. 

5. The purpose of the primary key is used to reference a row in a column. It needs to be unique otherwise it could be pointing to a different value than intended. 

Exercises: 

1. CREATE TABLE Customers (
   id INTEGER NOT NULL PRIMARY KEY AUTO_INCREMENT,
   firstName VARCHAR(255) NOT NULL,
   lastName VARCHAR(255) NOT NULL,
   address VARCHAR(255) NOT NULL,
   city VARCHAR(255) NOT NULL,
   state VARCHAR(2) NOT NULL,
   zip VARCHAR(5) NOT NULL UNSIGNED,
   email VARCHAR(2) NOT NULL,
);

2. ALTER TABLE Customers ADD age INTEGER NOT NULL UNSIGNED;

3. INSERT INTO Customers (firstName, lastName, address, city, state, zip, email) VALUES ('Terry','Yailer', '2876 W Milkyway', 'Springfield', 'EX', '99110', 'Tyailer@email.com');
INSERT INTO Customers (firstName, lastName, address, city, state, zip, email) VALUES ('Jerry','Yailer', '2876 W Milkyway', 'Springfield', 'EX', '99110', 'Jyailer@email.com');
INSERT INTO Customers (firstName, lastName, address, city, state, zip, email) VALUES ('Ferry','Yailer', '2876 W Milkyway', 'Springfield', 'EX', '99110', 'Fyailer@email.com');

4. SELECT * FROM Customers;

5. CREATE TABLE Products (
   id INTEGER NOT NULL PRIMARY KEY AUTO_INCREMENT,
   title VARCHAR(255) NOT NULL,
   desc VARCHAR(255) NOT NULL,
   price DECIMAL(5,2) NOT NULL,
) 

6. INSERT INTO Products(title, desc, price) VALUES('Water', 'You Thirsty?', 0.99);
INSERT INTO Products(title, desc, price) VALUES('Chips', 'You Hungry?', 0.99);
INSERT INTO Products(title, desc, price) VALUES('Combo', 'Why not both?', 1.50);

7. SELECT * FROM Products;

8. UPDATE Products SET price = 1.25 WHERE id = 3;

9. SELECT * FROM Products WHERE price < 100;

10.