> >> My question is whether postgres can index null values, and if not, do I

> >> have to accept a full table scan when locating records.
> >
> > It indexes them, but "is null" is not an indexable operator, so you
> > can't directly solve the above with a 3-column index.  What you can do
> > instead is use a partial index, for instance
> >
> > create index i on CUSTOMER.WCCustOrderStatusLog (WCOrderStatusID)
> > where Acknowledged is null and Processing is null;
>
> That's a very nifty trick and exactly the sort of answer I was after!

Add CREATE INDEX doc mention of using partial indexes for IS NULL
indexing;  idea from Tom.