Conceptual Questions 
1.  A RDBMS is a database management system designed specifically for relational databases.
2.  SQL is the language used to communicate with a database.
3.  An ER Model is a model that defines data elements and relationships for a specified system. 
4.  A one-to-one relationship is when a primary entity will have only one related entity. 
    A one-to-many relationship is when the primary entity may have many related entities. 
    A many-to-many relationship is when many entities from one table can be related to many entities from another table.
5. The purpose of a primary is to implement a relationship between tow tables, they are unique because they hold unique values.
SQL Exercises 
6.  CREATE TABLE IF NOT EXISTS customers (
    1. id INTEGER NOT NULL AUTO_INCREMENT PRIMARY KEY,
    2. first_name VARCHAR(255) NOT NULL,
    3. last_name VARCHAR(255) NOT NULL,
    4. address VARCHAR(255) NOT NULL,
    5. city VARCHAR(255) NOT NULL,
    6. state VARCHAR(255) NOT NULL,
    7. zip INTEGER(5) NOT NULL,
    8. email VARCHAR(255) NOT NULL );
7. ALTER TABLE customers
   ADD age INTEGER UNSIGNED NOT NULL;
8. INSERT INTO customers(first_name, last_name, address, city, state, zip, email) VALUES 
   ('Diego', 'Chavez', '435 Oak St', 'Bakersfield', 'Ca', '93314', 'diego@email.com'),
   ('John', 'Doe', '123 Elm St', 'Oakland', 'Ca', '92456', 'john@email.com'),
   ('Mary', 'Jane', '1800 L St', 'Los Angeles', 'Ca', '95678', 'mary@email.com');
9. SELECT * FROM customers;
10. CREATE TABLE IF NOT EXISTS products (
    1. id INTEGER NOT NULL AUTO_INCREMENT PRIMARY KEY,
    2. title VARCHAR(255) NOT NULL,
    3. description VARCHAR(255) NOT NULL,
    4. price DECIMAL(5,2) NOT NULL );
11. INSERT INTO products (title, description, price) VALUES
    ('nintendo switch', 'newest nintendo gaming device', '199.99'),
    ('ps4', 'newest sony gaming device', '249.99'),
    ('xbox one', 'newest microsoft device', '299.99');
12. SELECT * FROM products;
13. UPDATE products SET price = '200.00' WHERE id = 2;
14. SELECT products WHERE price < 100;
15. DELETE FROM products
    ORDER BY id desc limit 1;
16. CREATE TABLE IF NOT EXISTS orders ()
    1. id INTEGER NOT NULL AUTO_INCREMENT PRIMARY KEY,
    2. cid INTEGER UNSIGNED NOT NULL,
    3. amount DECIMAL UNSIGNED NOT NULL,
    4. date TIMESTAMP DEFAULT CURRENT_TIMESTOP,
    FOREIGN KEY (cid) REFERENCES customers(id) );
17. INSERT INTO orders(cid, amount, date) VALUES 
    ('1', '1', '2020-03-17 10:00:00'),
    ('2', '3', '2020-03-17 23:59:00'),
    ('3', '5', '2020-03-17 12:00:00');
18. SELECT orders WHERE id  = 1;
19. SELECT orders WHERE price > 100;
20. DROP TABLE IF EXISTS orders;