Re: data export has strange decimal values

On Wed, Dec 28, 2016 at 12:19 PM, Steve Crawford
<scrawford(at)pinpointresearch(dot)com> wrote:
>
>
> On Wed, Dec 28, 2016 at 9:41 AM, Marc Fromm <Marc(dot)Fromm(at)wwu(dot)edu> wrote:
>>
>> I’m using postgresql9.2. When I export some data using phppgadmin some
>> decimal values are exported as 9.4700003 instead of 9.47 (they show as 9.47
>> in phppgadmin and when displayed on the web. Others export as 9.5299997
>> instead of 9.53 (again they show as 9.53 in phppgadmin and when displayed on
>> the web).
>>
>>
>>
>> The data type for the field is set as type “real.” Is this data type
>> causing the problem and I should change it to decimal?
>>
>>
>>
>> What could be creating this plus or minus 0.0000003 to the recorded value?
>>
>
>
> https://www.postgresql.org/docs/9.6/static/datatype-numeric.html
>
> "The data types real and double precision are inexact, variable-precision
> numeric types. In practice, these types are usually implementations of IEEE
> Standard 754 for Binary Floating-Point Arithmetic (single and double
> precision, respectively), to the extent that the underlying processor,
> operating system, and compiler support it.
>
> Inexact means that some values cannot be converted exactly to the internal
> format and are stored as approximations, so that storing and retrieving a
> value might show slight discrepancies. Managing these errors and how they
> propagate through calculations is the subject of an entire branch of
> mathematics and computer science and will not be discussed here..."

Yeah if OP wants exact numbers he needs to use numeric type.