Yet another very common error is when someone puts a wrong condition in a WHERE clause and that essentially renders an outer join into an inner join. A great advice on coding predicates in outer joins comes from a DB2 expert Terry Purcell.

"Meet the experts: Terry Purcell on coding predicates in outer joins: A comparison of simple outer join constructs"

http://www.ibm.com/developerworks/db2/library/techarticle/purcell/0112purcell.html

Enjoy!