Re: Why count(*) doest use index?

[Willy-Bas Loos <willybas@xxxxxxxxx>]

Other well known dbms's do have this possibility, because they place deleted or updated records in a separate table or file (plz correct me if i'm wrong). But this has other, greater performance disadvantages. The count(*) problem is a bit of a publicity problem rather than a real performance problem (i've been told). People are aware of the fact that count(*) is faster in other dbms's, but "we" don't want superficial things like optimizing count(*) for publicity ruin other, more important things for us, performance-wise.

On Sat, Mar 5, 2011 at 11:46 PM, John R Pierce <pierce@xxxxxxxxxxxx> wrote:

On 03/05/11 2:05 PM, Allan Kamau wrote:

Is it possible in theory to efficiently perform count the primary or
unique indices underlying data structures, regardless whether there is
a WHERE clause detailing filtration base on values from such index or
not?

indexes are not exact, due to possibly constant changes in the current number of visible elements in the relation.





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