In the SQL outer JOIN all the content of the both tables are integrated together either they are matched or not.
If you take an example of employee table
Outer join of two types:
1.Left outer join (also known as left join): this join returns all the rows from left table combine with the matching rows of the right table. If you get no matching in the right table it returns NULL values.
2.Right outer join (also known as right join): this join returns all the rows from right table are combined with the matching rows of left table .If you get no column matching in the left table .it returns null value.
This diagram shows the different type of joins: