PROC SQL: Beyond the Basics Using SAS®

7.6. Outer Joins

As the previous examples in this chapter have shown, an inner join disregards any rows where the search condition is not met. This differs significantly from the way an outer join groups tables. In contrast with an inner join, an outer join keeps rows that match the ON (search) condition, as well as preserving some or all of the unmatched data from one or both of the tables. Essentially, an outer join retains rows from one table even when they do not match rows in the second table. This distinction is critical because this is what truly differentiates an outer join from an inner join.

Next, an outer join is capable of processing a maximum of two tables at a time, whereas (under the SAS implementation) an inner join is able to ...