Re: [HACKERS] Dates BC.

Karel Zak wrote:
> On Fri, Dec 19, 2003 at 01:12:08AM -0800, Dann Corbit wrote:
> > There is no zero calendar year. The first year of Anno Domini is 1. It's ordinal, not cardinal.
>
> I agree. But the follow quoted code is not use in date_part() there
> Kurt found bug. It's used in to_timestamp() _only_, and it works,
> because tm2timestamp() and date2j() work with zero year.
>
> > > Is there connection between formatting.c and date_part() ?
> > > I don't think so...
> > >
> > > > In backend/utils/adt/formatting.c:
> > > >
> > > > if (tmfc.bc)
> > > > {
> > > > if (tm->tm_year > 0)
> > > > tm->tm_year = -(tm->tm_year - 1);
>
>
> ... "tm->tm_year = -(tm->tm_year - 1)" is used for:
>
> # select to_timestamp('0001/01/01 BC', 'YYYY/MM/DD AD');
> to_timestamp
> ------------------------
> 0001-01-01 00:00:00 BC
>
> and it's OK.
>
>
> I think a bug is somewhere in timestamp2tm() which used in next
> examples and it's shared between more functions:
>
> # select to_char('0001-01-01 BC'::date, 'YYYY/MM/DD AD');
> to_char
> ---------------
> 0000/01/01 AD
>
> # SELECT EXTRACT(YEAR from '0001-01-01 BC'::date);
> date_part
> -----------
> 0

Very interesting. I am attaching a patch that fixes these cases.
There were two bugs in our code:

o date_part didn't handle BC years properly (must -1 year)
o formatting code tested for BC dates as only < 0, not <= 0

Look at this before and after test output. The attached patdch fixes
this. Regression tests pass.

---------------------------------------------------------------------------

BEFORE:

test=> SELECT EXTRACT(YEAR from '0002-01-01 AD'::date);
date_part
-----------
2
(1 row)

test=> SELECT EXTRACT(YEAR from '0001-01-01 AD'::date);
date_part
-----------
1
(1 row)

test=> SELECT EXTRACT(YEAR from '0001-01-01 BC'::date);
date_part
-----------
0 **error**
(1 row)

test=> SELECT EXTRACT(YEAR from '0002-01-01 BC'::date);
date_part
-----------
-1 **error**
(1 row)

test=> select to_char('0002-01-01 AD'::date, 'YYYY/MM/DD AD');
to_char
---------------
0002/01/01 AD
(1 row)

test=> select to_char('0001-01-01 AD'::date, 'YYYY/MM/DD AD');
to_char
---------------
0001/01/01 AD
(1 row)

test=> select to_char('0001-01-01 BC'::date, 'YYYY/MM/DD AD');
to_char
---------------
0000/01/01 AD **error in year and AD**
(1 row)

test=> select to_char('0002-01-01 BC'::date, 'YYYY/MM/DD AD');
to_char
---------------
0002/01/01 BC
(1 row)

---------------------------------------------------------------------------

AFTER:

test=> SELECT EXTRACT(YEAR from '0002-01-01 AD'::date);
date_part
-----------
2
(1 row)

test=> SELECT EXTRACT(YEAR from '0001-01-01 AD'::date);
date_part
-----------
1
(1 row)

test=> SELECT EXTRACT(YEAR from '0001-01-01 BC'::date);
date_part
-----------
-1
(1 row)

test=> SELECT EXTRACT(YEAR from '0002-01-01 BC'::date);
date_part
-----------
-2
(1 row)

test=> select to_char('0002-01-01 AD'::date, 'YYYY/MM/DD AD');
to_char
---------------
0002/01/01 AD
(1 row)

test=> select to_char('0001-01-01 AD'::date, 'YYYY/MM/DD AD');
to_char
---------------
0001/01/01 AD
(1 row)

test=> select to_char('0001-01-01 BC'::date, 'YYYY/MM/DD AD');
to_char
---------------
0001/01/01 BC
(1 row)

test=> select to_char('0002-01-01 BC'::date, 'YYYY/MM/DD AD');
to_char
---------------
0002/01/01 BC
(1 row)

--
Bruce Momjian | http://candle.pha.pa.us
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