Re: group by

On Fri, 3 Oct 2003, Kathy Zhu wrote:

> Hi,
>
> I notices a weird thing here.
>
> version 7.2.1
> on Solaris
>
> table "test", has a field "state".
> There are 4 "state" values, 1, 2, 3, 4.
>
> select count(*) from test group by state;
> took 11500 msec
>
> but
>
> select count(*) from test where state = 1;
> select count(*) from test where state = 2;
> select count(*) from test where state = 3;
> select count(*) from test where state = 4;
> total took 626 msec
>
> Why ??

First thought was caching: the disk blocks are cached in memory after the first
qery so all the others just fetch from there.

Second thought: well I haven't really had it but indexes and sorting is sort of
sloshing around in my mind. Not sure how that applies to here since I can't
remember if the first would require the sort step having retrieved all the
tuples and the others would just use the index pages.

It is Friday though.

--
Nigel J. Andrews