Re: sum divided by count ends in zero - Mailing list pgsql-novice

From Dara Olson
Subject Re: sum divided by count ends in zero
Date
Msg-id D0666F34C95145368966E0CDE521A815@GISWKSTN
Whole thread Raw
In response to sum divided by count ends in zero  ("Dara Olson" <dolson@glifwc.org>)
List pgsql-novice
Thank you so very much!
Dara
----- Original Message -----
From: naptrel
Sent: Wednesday, November 25, 2009 2:59 AM
Subject: Re: [NOVICE] sum divided by count ends in zero

Hi Dara,

I suspect that the problem is that the division is acting on two integers, and doing integer division.

If you have two integers, a=3 and b=10, then:
a+b = 13
a*b = 30
b-a = 7

but:

b/a = 3   because 3 will fit 3 times into 10, with 1 remaining (i.e. b % a = 1)
a/b = 0   because the result is also an integer, and 10 will not go into 3 (note: a %b = 3)

You need to 'cast' the variables a and b to floating point values so that the division produces a floating point result

E.g.:

a::float / b::float = 0.3

Nathaniel


On 24 Nov 2009, at 22:32, Dara Olson wrote:

Greetings.
 
I am having a problem dividing a sum by a count and end up with zero, however I am able to multiply, subtract and add. 
 
Here are samples of the two views:
View that groups individuals into specific groups by numbers:
SELECT
SUM(CASE when indiv_total_lbs <= 50 then 1 else 0 end) as "0_50",
SUM(CASE when indiv_total_lbs <= 100 AND indiv_total_lbs > 50 then 1 else 0 end) as "51_100", etc.
FROM wr_harvest.sh_sum_by_harvestor
 
View that gathers overall stats:
SELECT
AVG (indiv_total_trips) AS ave_no_trips, etc.
COUNT(DISTINCT x) AS no_harvestors, etc.
FROM wr_harvest.sh_sum_by_harvestor
 
I want to find the percent of individuals in each catagory from the first view.
SELECT  
a."0_50"/b.no_harvestors *100 AS "0_50percent",
a."51_100"/b.no_harvestors *100 AS  "51_100percent", etc
FROM wr_harvest.sh_distribution_stats_no as a, wr_harvest.sh_harvestor_stats as b
 
I am able to add, subtract and mulitply the values with the correct outcomes, but every time I try to divide the two numbers I end in zero. 
What am I doing wrong?  Any help would be greatly appreciated.
 
Miigwech in advance!
Dara
 

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