1* A relational database management system (RDBMS) is a program that lets you create, update, and administer a relational database. SQL stands for Structured Query Language which main purpose is to access the database.
2* You need to add a primary key when you want to use unique id number for example to join tables, or you don't want to keep identical records.
3* Foreign Key is the name given to a table column that references the primary key on another table.
4* We need a third table that will keep ids of those two tables in order to have a many to many relationship between two tables.
5* SELECT * FROM table_name; is used to retrieve data from a table.
6* WHERE is used to filter the results of a query.
7* View is a virtual table created from a stored query in the DB. With view you can show only a subset of the data, can join multiple tables into a single view and can aggregate data in a view. View don't actually hold data. Use case - displaying only active users on a website.