How do I change sort order behavious with nulls

Dear list,

is there a simple way to change the way ORDER BY works on columns with 
NULLs? I can understand the need for default behaviour but there must be 
cases when this is undesirable. I have such a query with the NULLs arising 
as the result of an OUTER JOIN and I would like to ORDER BY DESC with 
NULLs treated as <= 0. I've already tried a few things but nothing's 
working so far.

Thanx for any pointers.

Charlie

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Charlie Clark