Thread: sum divided by count ends in zero

----- Original Message -----

From: naptrel

To: Dara Olson

Cc: pgsql-novice@postgresql.org

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