Re: Should "select 'nan'::float = 'nan'::float;" return false as per IEEE 754

On 10/28/2012 11:05 AM, Chris Corbyn wrote:
> Would this introduce problems finding rows where the stored value is NaN? You'd need to add a function or operator to
avoidthat.
 
I guess it should behave similar to NULL-s

That is IS NOT DISTINCT FROM should still return true

test=# select NULL IS NOT DISTINCT FROM NULL as must_be_true; must_be_true
-------------- t
(1 row)

I guess making the NaN comparison IEEE compliant could introduce
some problems with indexes, so I propose that index operators would
treat NaNs like NULLs


Hannu

> Il giorno 28/ott/2012, alle ore 20:43, Hannu Krosing ha scritto:
>
>> This is how PostgreSQL currently works -
>>
>> test=# select 'NaN'::float = 'NaN'::float as must_be_false;
>> must_be_false
>> ----------
>> t
>> (1 row)
>>
>> I think that PostgreSQL's behaviour of comparing two
>> NaN-s as equal is wrong and Iwe should follow the IEEE 754 spec here
>>
>> As per IEEE 754 a NaN behaves similar to NULL in SQL.
>>
>> There is some discussion of why it is so at:
>>
>>
http://stackoverflow.com/questions/1565164/what-is-the-rationale-for-all-comparisons-returning-false-for-ieee754-nan-values
>>
>> especially the first comment
>>
>> ---------
>> Hannu
>>
>>
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