In MySQL syntax, LEFT OUTER JOIN and LEFT JOIN are identical: (from http://dev.mysql.com/doc/refman/5.0/en/join.html)
| table_reference {LEFT|RIGHT} [OUTER] JOIN table_reference join_condition
| table_reference NATURAL [{LEFT|RIGHT} [OUTER]] JOIN table_factor
Note that the OUTER keyword is optional for LEFT/RIGHT JOIN.
LEFT and RIGHT joins are both outer joins. I believe there are some flavors of SQL that may require the OUTER keyword, but MySQL does not. That is to say that at times LEFT JOIN may not be valid.
