The join clause allows us to combine SQL tables. Tables can be combined in different ways. Think on inner join as an intersection of two tables and an outer join as a union of two tables. This table explains different types of joins.

We will be using the following two tables in the examples:

The goal of database normalization is to reduce data redundancy and to improve data integrity. This is done by organizing columns and tables by apply the normal forms. In theoretical database speak, a table is called a relation and a column is called an attribute.