Predicates at ON-clause and WHERE-clause

I sometimes came across queries that were written by other developers who put predicates at the ON-clause... I seems have difficulty telling the difference between the On-clause predicate and WHERE-clause predicate... Googled around that found the following useful documents: 1. http://www.catterallconsulting.com/2009/07/outer-join-get-predicates-right.html 2.http://www.ibm.com/developerworks/data/library/techarticle/purcell/0112purcell.html 3. http://richardlees.blogspot.com/ Sunday, June 14, 2009 The subtlety of SQL must be appreciated...