Re: sum multiple tables gives wrong answer?

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Тема Re: sum multiple tables gives wrong answer?
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Msg-id 3AEE0ADFAD174B90BD470E6D812D0333@marktestcr.marktest.pt
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Ответ на sum multiple tables gives wrong answer?  ("Michael Diener" <m.diener@gomogi.com>)
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Howdy, Michael.
 
Your query is failing because you are doing the cartesian product of the tables with that query
Can't you do it on two different queries?
 
Say
select  sum(flaeche)/10000 as "greens HA"  from green;
and then
select  sum(flaeche)/10000 as "fairway HA"  from fairway;
?
 
Do you really need one single query?
 
If so, try this
 

select

 (sum(green.flaeche)/10000) / count(fairway.*) as "greens HA",

 (sum (fairway.flaeche)/10000) / count(green.*) as "fairway HA"

  from green, fairway;

 
NB: This is untested code, it might contain syntactic/semantic bugs.
 
Best,
Oliveiros Cristina
 
----- Original Message -----
Sent: Wednesday, June 02, 2010 3:23 PM
Subject: [NOVICE] sum multiple tables gives wrong answer?

Hi,

 

I’m new to the list and have the following situation happening "PostgreSQL 8.4.1, compiled by Visual C++ build 1400, 32-bit" running windows XP sp3

 

I have an SQL problem that I thought was easy to do but gives me always the wrong answer.

 

2 Tables with a column called “flaeche” “double precision”, in English  “area” and I want to sum up the values for flaeche in each table to give me the total area for flaeche in each table.

 

Correct answer comes with this sql

select  sum(flaeche)/10000 as "greens HA"  from green;

 

result:

greenHA

1.25358085

 

Wrong Answer with this query

select

 sum(green.flaeche)/10000 as "greens HA",

 sum (fairway.flaeche)/10000 as "fairway HA"

  from green, fairway;

 

result:

green HA                   fairway HA

48.8896531                 508.94143659

 

Fairway correct answer is  14.96886578 HA

Green correct answer is 1.25358085  HA

 

What is going on ??

 

Cheers

michael

 

Michael Diener

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