What is a FULL OUTER Join?
A FULL OUTER join operation on two record sets returns all of the records contained in both sets even if they do not meet the join criteria. For each record returned that does not have matching records in the corresponding set, a NULL value will be returned for each column selected from the corresponding set. When you join two tables you can think of the records involved falling into three different unique record sets. The first record set contains only those records meeting the join criteria. This is the set produced when you perform an INNER JOIN. The second set of records is the set of records in the left table that do not meet the join criteria, or are said to not have matching records in the right table. And the last set of records is the set of records in the right table that do not have matching records in the left table. The following diagram illustrates the three different sets: Click for larger image In the above diagram, the two tables are represented by the two circles, lab
