Re: PostgreSQL needs percentage function

Em 18/12/2017 14:28, Michael Nolan escreveu:
>
>
> On Mon, Dec 18, 2017 at 6:23 AM, Nick Dro <postgresql(at)walla(dot)co(dot)il
> <mailto:postgresql(at)walla(dot)co(dot)il>> wrote:
>
> Hi,
> Why PostgreSQL doesn't have build-in function to calculate
> percentage? somthing like percent(number,%
> for example:
> select percent(100,1) will calculate 1% of 100 = 1
> select percent(25,20) will calculate 20% of 25 = 5
> Seems like a nice addition to the math functions list:
> https://www.postgresql.org/docs/9.5/static/functions-math.html
> <https://www.postgresql.org/docs/9.5/static/functions-math.html>
> This is veryhelpull function, many uses percentage calculation in
> thier work and it will simplify the process. Percentage
> calculation is considered a basic math operation and I think
> postgresql should support it as a build-in function.
> Seems like easy to implment isn't it?
>
>
> It's a bit trickier than that, because you';ll have to deal with
> integers, real, double precision, etc.  You may also want to deal with
> null values.  I found it more useful to write a function that displays
> X as a percentage of Y, rounded to 1 digit to the right of the decimal
> point.
> --
> Mike Nolan

I believe that having a built-in function for percentage is not a good
idea. Is just like having a function to calculate fractions... Someone
would like to have percentages as 0..1, others would like to have it
multiplied by 100. How to deal with integers? And so on (as others
already stated here).

But, is it possible to have a aggregate function that calculates de
percent from the sum (and/or count) total (as a value from 0 ... 1) for
numeric (or double)?

Looking really superficially seems to me that would be a great addition
to the aggreggates (and is not just a trivial div/multiply op)

Edson