| From: | Greg Stark <gsstark(at)mit(dot)edu> |
|---|---|
| To: | John Sidney-Woollett <johnsw(at)wardbrook(dot)com> |
| Cc: | Carlos Oliva <carlos(at)pbsinet(dot)com>, pgsql-general(at)postgresql(dot)org |
| Subject: | Re: Backwards index scan |
| Date: | 2006-06-06 21:48:12 |
| Message-ID: | 87zmgq7y77.fsf@stark.xeocode.com |
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| Thread: | |
| Lists: | pgsql-general |
John Sidney-Woollett <johnsw(at)wardbrook(dot)com> writes:
> I don't think that null values are indexed - you'll probably need to coalesce
> your null data value to some value if you want it indexed.
That is most definitely not true for Postgres. NULL values are included in the
index.
However NULLs sort as greater than all values in Postgres. So when you sort
descending they'll appear *first*. If you sort ascending they'll appear last.
If you have any clauses like 'WHERE col > foo' then it will not be true for
NULL values of col regardless of what foo is and those records will be
dropped. This is true regardless of whether there's an index.
--
greg
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