The outer join is an extension of the inner join that includes both rows that qualify for a simple inner join as well as a specified set of rows that do not match the join conditions expressed by the query.
Because outer joins are as complicated to code correctly as they are to interpret, this section studies them in detail, including a carefully thought out case study and series of recommendations contributed by a database administrator.
There are three types of outer joins:
- LEFT OUTER JOIN (see Left Outer Join)
- RIGHT OUTER JOIN (see Right Outer Join)
- FULL OUTER JOIN (see Full Outer Join)