Bruce Momjian <pgman@candle.pha.pa.us> writes:
> I know we index NULL values in multi-column indexes, but do we
> currently even store the rows that have only NULLs in a the index.
btree does. I don't think any of the other index AMs do. hash could
probably be made to without much trouble (just decree a hash value,
say zero, for nulls). But I dunno what rtree or gist would do with a
leading-column null.
regards, tom lane