Re: [GENERAL] Problems with inequalities on numeric fields in 6.5

Bruce Momjian wrote on Wed, 07 Jul 1999 04:07:00 EDT
>> lmc=> explain select count(*) from lmctot where j_m>'3.4' and j_m<'3.5';
>> NOTICE:  QUERY PLAN:
>>
>> Aggregate  (cost=62349.97 rows=788100 width=4)
>>   ->  Index Scan using j on lmctot  (cost=62349.97 rows=788100 width=4)
>>
>>
>Please try this:
>
> lmc=> explain select count(*) from lmctot where j_m>3.4::float4 and
> j_m<3.5::float4
>
>Also, given your min/max, I am not sure why it thinks it is going to get
>788,100 rows.  How many rows in the table again?
>
>Does (3.5-3.4)/(max-min) * #rows = 788k?
>

Thanks, Bruce!

Yes, I tried the latter query and it's the same:

--------------------------------------------------

lmc=> explain select count(*) from lmctot where j_m>3.4::float4 and j_m<3.5::float4;
NOTICE:  QUERY PLAN:

Aggregate  (cost=62349.97 rows=788100 width=4)
  ->  Index Scan using j on lmctot  (cost=62349.97 rows=788100 width=4)

EXPLAIN

--------------------------------------------------
I've tried all permutations of the conversions in the ranges with
similar results (and vacuum analyzed several times as well as
dumped and reloaded and reloaded from scracth).  We have
a larger database with 20M rows which has a similar behavior.

There are 7092894 rows in database "lmc".  So:

(3.5-3.4)/(99.999-2.731) = 7292.1 != 788k

A clue?

Thanks again,

--M

===========================================================================

Martin Weinberg                      Phone: (413) 545-3821
Dept. of Physics and Astronomy       FAX:   (413) 545-2117/0648
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