| From: | Pedro Gimeno <pgsql-004(at)personal(dot)formauri(dot)es> |
|---|---|
| To: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com> |
| Cc: | Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Pedro Gimeno <pgsql-004(at)personal(dot)formauri(dot)es>, rschaaf(at)commoninf(dot)com, pgsql-bugs(at)postgresql(dot)org |
| Subject: | Re: Re: BUG #12885: The result of casting a double to an integer depends on the database version |
| Date: | 2015-03-27 17:53:11 |
| Message-ID: | 55159907.1060809@personal.formauri.es |
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| Lists: | pgsql-bugs |
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.
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