1. A relational database management system (RDBMS) is a DBMS designed specifically for relational databases. 
A relational database refers to a database that stores data in a structured format, using rows and columns.
 This makes it easy to locate and access specific values within the database.
 It is "relational" because the values within each table are related to each other.
 Tables may also be related to other tables.
 The relational structure makes it possible to run queries across multiple tables at once.  

2. SQL stands for Structured Query Language. 
SQL is used to communicate with a database.
SQL statements are used to perform tasks such as update and/or retrieve data on a database.
 It is the standard language for relational database management systems.

3. Entity Relational (ER) Model is a high-level conceptual data model diagram. 
ER modeling helps you to analyze data requirements systematically to produce a well-designed database.

4. One-to-One (1-1) relationship is defined as the relationship between two tables where both the tables 
should be associated with each other based on only one matching row. 
This relationship can be created using Primary key-Unique foreign key constraints.
The One-to-Many relationship is defined as a relationship between two tables where a row from one table 
can have multiple matching rows in another table. This relationship can be created using Primary 
key-Foreign key relationship.
A many-to-many relationship occurs when multiple records in a table are associated with multiple records in another table. 

5. A primary key is a field in a table which uniquely identifies each row/record in a database table. 
Primary keys must contain unique values. 
A primary key column cannot have NULL values.

6. CREATE TABLE IF NOT EXISTS customers (
    id INTEGER NOT NULL AUTO_INCREMENT,
    firstName VARCHAR(30) NOT NULL,
    lastName VARCHAR(30) NOT NULL,
    address VARCHAR(100) NOT NULL,
    city VARCHAR(100) NOT NULL,
    state CHAR(2) NOT NULL,
    zip INTEGER(5) UNSIGNED NOT NULL,
    email VARCHAR(100) NOT NULL,
    PRIMARY KEY (id)
    );

7. ALTER TABLE customers ADD age INTEGER UNSIGNED NOT NULL
 
8. INSERT INTO customers(id, firstname, lastname, address, city, state, zip, email, age) VALUES(1, 'Thomas', 'Mackey', '2353 Yellow Ave', 'Pomona', 'CA', 91765, 'ewwe@csub.edu', 34);

INSERT INTO customers(id, firstname, lastname, address, city, state, zip, email, age) VALUES(2, 'Quincy', 'Oneal', '9034 Flower Dr', 'Tuskegee', 'AL', 36088, 'rego@gmail.com', 20);

INSERT INTO customers(id, firstname, lastname, address, city, state, zip, email, age) VALUES(3, 'Michelle', 'Klaud', '9217 Peppermint Ln', 'Houston', 'TX', 77005, 'hollypop@yahoo.com', 12);

9. SELECT * FROM customers;

10. 
CREATE TABLE IF NOT EXISTS products (
    id INTEGER NOT NULL AUTO_INCREMENT,
    title VARCHAR(1000) NOT NULL,
    description VARCHAR(1000) NOT NULL,
    price DECIMAL(5,2) UNSIGNED NOT NULL,
    PRIMARY KEY (id)
    );
 
11.  INSERT INTO products(id, title, description, price) VALUES(1, 'King Size Bed', 'Get this mattress, fit for a king!', 428.12);

INSERT INTO products(id, title, description, price) VALUES(2, 'Golden Retriever', 'Live your life like it is golden with this iconic pooch.', 312.91);

INSERT INTO products(id, title, description, price) VALUES(3, '1999 Toyota Camry', 'Drive like a boss.', 999.75);

12. SELECT * FROM products;

13. UPDATE products SET price = 49.99 WHERE id = 3;

14. SELECT * FROM products WHERE price < 100;

15. DELETE from products ORDER BY id DESC LIMIT 1;

16. CREATE TABLE IF NOT EXISTS orders (
    id INTEGER NOT NULL AUTO_INCREMENT,
    cid INTEGER NOT NULL,
    amount DECIMAL(5,2) UNSIGNED NOT NULL,
    dt TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    PRIMARY KEY (id),
    FOREIGN KEY (cid) REFERENCES customers(id)
    );

17. INSERT INTO orders(id, cid, amount) VALUES(1, 1, 500.00);
INSERT INTO orders(id, cid, amount) VALUES(2, 2, 400.00);
INSERT INTO orders(id, cid, amount) VALUES(3, 3, 20.00);

18. SELECT * FROM orders WHERE cid = 1; 

19. SELECT * FROM orders WHERE amount > 100;

20. DROP TABLE IF EXISTS orders;