1. A Relational Database Management System (RDBMS) 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. An SQL (Structured Query Language) is a programming language used to 
communicate with data stored in a RDBMS. It is the most common standardized 
language used to access databases. It allows you to perform operations like 
"Create", "Select", "Insert", "Update", and "Delete" on data and tables in 
a database.

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

4. One-to-one Relationship: 1 entity from entity set X can be associated 
   with at most 1 entity of entity set Y and vice versa.
   
   One-to-many Relationship: 1 entity from entity set X can be associated
   with multiple entities of entity set Y, but an entity from set Y can be
   associated with at least one entity.

   Many-to-many Relationship: 1 entity from X can be associated with more 
   than 1 entity from Y and vice versa.

5. The main purpose of a primary key is to implement a relationship between
two tables in a RDBMS. More specifically, it is the "target" which a foreign
key can reference. Primary keys must contain unique values, especially if the
key consists of multiple columns.

6. CREATE TABLE IF NOT EXISTS Customers (
    id INTEGER NOT NULL 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 INTEGER(5) UNSIGNED NOT NULL,
    email VARCHAR(255) NOT NULL,
    PRIMARY KEY (id)
);

7. ALTER TABLE Customers ADD Age INT UNSIGNED

8. INSERT INTO Customers (CustomerName, PhoneNumber, Email)

9. SELECT firstName, lastName FROM Customers WHERE zip = 93309

10. CREATE TABLE IF NOT EXISTS Products (
    id INTEGER NOT NULL AUTO_INCREMENT,
    title VARCHAR(255) NOT NULL,
    description VARCHAR(255) NOT NULL,
    price DECIMAL(5, 2) UNSIGNED NOT NULL 
    PRIMARY KEY (id)
);

11. INSERT INTO Products (ProductName, SerialNumber, Color)

12. SELECT id, title FROM Products WHERE price = 0.99

13. UPDATE Products SET id = 5101 WHERE price = 49.99