Re: count * performance issue

[Mark Mielke <mark@xxxxxxxxxxxxxx>]

Robins Tharakan wrote:

Hi,

I have been reading this conversation for a few days now and I just wanted to ask this. >From the release notes, one of the new additions in 8.3 is (Allow col IS NULL to use an index (Teodor)).

Sorry, if I am missing something here, but shouldn't something like this allow us to get a (fast) accurate count ?

SELECT COUNT(*) from table WHERE indexed_field IS NULL
+
SELECT COUNT(*) from table WHERE indexed_field IS NOT NULL

For PostgreSQL: You still don't know whether the row is visible until you check the row. That it's NULL or NOT NULL does not influence this truth.

Cheers,
mark

-- 
Mark Mielke <mark@xxxxxxxxx>