ASA SQL User's Guide
  Joins: Retrieving Data from Several Tables

Inner and outer joins

The keywords INNER, LEFT OUTER, RIGHT OUTER, and FULL OUTER may be used to modify key joins, natural joins, and joins with an ON phrase. The default is INNER. The keyword OUTER is optional. These modifiers do not apply to cross joins.

Inner joins
Outer joins
Transact-SQL outer joins (*= or =*)