Previously, we had looked at inner join, where we select rows common to the participating tables to a join. One case is that if we are interested in selecting elements in a table regardless of whether they are present in the second table? We will now need to use the SQL OUTER JOIN command.

The syntax for performing an outer join in SQL is database-dependent. For example, in Oracle, we will place an "(+)" in the WHERE clause on the other side of the table for which we want to include all the rows.

Let's we have the following two tables,

If we want to find out sales by region. We see that table Geography includes information on regions and stores, and table Store_Information contains sales information for each store. To get the sales information by region, we have to combine the information from the two tables. Examining the two tables, we find that they are linked via the common field, "store_name".

Note: When there is no match on the second table NULL is returned . In this case, "New York" does not appear in the table Store_Information, thus its corresponding "SALES" column is NULL.