Обсуждение: Problem with zero year

We added the following commit in 8.4:
/src/backend/utils/adt/datetime.c                                                                      tgl Reject year
zeroduring datetime input, except when it's a 2-digit year (then it means 2000 AD).  Formerly we silently interpreted
thisas 1 BC, which at best is unwarranted familiarity with the implementation. It's barely possible that some app
somewhereexpects the old behavior, though, so we won't back-patch this into existing release branches.
 

The problem is that the 2-digit year check is for <=2 digits, not
exactly two digits:
   /*    * When processing a year field, mark it for adjustment if it's only one    * or two digits.    */   if (*tmask
==DTK_M(YEAR))       *is2digits = (flen <= 2);
 

This leads to some unexpected outputs:
test=> select '1-1-0'::date;   date------------ 2000-01-01
test=> select '1-1-0 BC'::date;ERROR:  date/time field value out of range: "1-1-0 BC"LINE 1: select '1-1-0 BC'::date;
           ^
 
test=> select '1-1-0 AD'::date;    date------------ 2000-01-01
test=> select '1-1-000'::date;ERROR:  date/time field value out of range: "1-1-000"LINE 1: select '1-1-000'::date;

I think the BC part is fine because that can't possibily be 2000 AD, but
having '0' interpreted as 2000 seems counter to the commit message text;
should the assignment be changed to:
   if (*tmask == DTK_M(YEAR))       *is2digits = (flen == 2);

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + If your life is a hard drive, Christ can be your backup. +

Bruce Momjian <bruce@momjian.us> writes:
> The problem is that the 2-digit year check is for <=2 digits, not
> exactly two digits:
> ...
> This leads to some unexpected outputs:

>     test=> select '1-1-0'::date;
>        date
>     ------------
>      2000-01-01

We've interpreted that like that since 7.4, without complaints; and
I think it was an intentional change then (since 7.3 doesn't accept it).
I do not recommend changing it.
        regards, tom lane

Tom Lane wrote:
> Bruce Momjian <bruce@momjian.us> writes:
> > The problem is that the 2-digit year check is for <=2 digits, not
> > exactly two digits:
> > ...
> > This leads to some unexpected outputs:
> 
> >     test=> select '1-1-0'::date;
> >        date
> >     ------------
> >      2000-01-01
> 
> We've interpreted that like that since 7.4, without complaints; and
> I think it was an intentional change then (since 7.3 doesn't accept it).
> I do not recommend changing it.

OK, the release note text will be:
Reject year '0 BC' and years '000' and '0000' (Tom)  Previously these were interpreted as 1 BC.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + If your life is a hard drive, Christ can be your backup. +