Re: is it possible in pl/sql?
- From: Mark Bole <makbo@xxxxxxxxxxx>
- Date: Tue, 15 Feb 2005 09:47:55 -0800
Mark Bole wrote:
> Looney, Jason wrote:
>
>
>>My understanding was in the past count(*) returned a count of all non-null
>>rows, where count(1) (or any constant) returned a count of all rows. I just
>>verified this with 10g and this is not the case. The performance difference
>>was to perform a full table scan, instead of counting leaf blocks in a
>>primary key index or something like that. So maybe this was true in 6 or 7?
>>
>>
>
> [...]
>
> For what it's worth, my recollection is the same
>
Hmmm.. from "Oracle Performance Tuning 2nd edition" (Gurry and Corrigan,
O'Reilly Press, 1996) -- so were talking version 7 RBO here:
"Contrary to popular belief, COUNT(*) is faster than COUNT(1). If the
rows are being returned via an index, counting the index column--for
example, COUNT(EMP_NO) is faster still. [followed with actual test runs
including timings to prove this]"
So, for the sake of historical accuracy (and not much else), there is
some evidence that a long time ago the count(*) performance issue existed.
-Mark Bole
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