Re: Re: BUG #12885: The result of casting a double to an integer depends on the database version

On Sat, Mar 28, 2015 at 2:53 AM, Pedro Gimeno
<pgsql-004@personal.formauri.es> wrote:
> Michael Paquier wrote, On 2015-03-27 13:32:
>
>> Attached is a patch that adds nearest-to-even rounding for numeric
>> when dscale = 0. This gives the following results with the previous
>> query:
>
> That produces some quite surprising results:
>
> =# select '2.5'::numeric(9,0)::numeric(9,1),
>          '2.25'::numeric(9,1)::numeric(9,2),
>         '2.225'::numeric(9,2)::numeric(9,3),
>        '2.2225'::numeric(9,3)::numeric(9,4),
>       '2.22225'::numeric(9,4)::numeric(9,5);
>  numeric | numeric | numeric | numeric | numeric
> ---------+---------+---------+---------+---------
>      2.0 |    2.30 |   2.230 |  2.2230 | 2.22220
> (1 row)
>
> That rounding is inconsistent: since DEC_DIGITS is 4 by default, numbers
> with a number of digits which is a multiple of 4 + 1 will be rounded to
> nearest or even, and numbers with a different number of digits will be
> rounded up on a tie. And I have not tested, but apparently when
> DEC_DIGITS == 1 (array elements are single digits rather than packing
> several) it always rounds down on a tie.

Yeah, I forgot a check on dscale = 0 when deciding to carry to the
upper digit or not.
--
Michael