Dates BC.

Kurt Roeckx wrote:

I find this a little strange:

select date_part('year', '0002-01-01 BC'::date);
date_part
-----------
-1

It seems 1 BC and 0 are the same year.

In backend/utils/adt/formatting.c:

if (tmfc.bc)
{
if (tm->tm_year > 0)
tm->tm_year = -(tm->tm_year - 1);

It this normal or a bug?

Uh, well, yea, there was no year 0. However, it seems we should return
the proper year. My guess is that missing year 0 is the cause, and
there are certain reasons year 2 BC should return -1. If you are
subtracting dates, like 32AD - 4BC, you get 35, which is the proper
number of years spanned.

I am not sure what is the proper answer. I thought date_part just
grabbed "parts of the date" like it says, but obviously not, and there
are some good reasons for it, I guess.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

In article <20031218131120.GA11684@ping.be> you wrote:

I find this a little strange:

select date_part('year', '0002-01-01 BC'::date);
date_part
-----------
-1

It seems 1 BC and 0 are the same year.

There is an unresolveable legacy problem here, in that Brahmagupta did
not yet invent the mathematical concept of 0 until ~ 598 CE, by which
time the Roman Empire had fallen (depending on whether you believe it
actually fell). We'll just have to live with some weirdness on this
one. :)

Cheers,
D
--
David Fetter david@fetter.org http://fetter.org/
phone: +1 510 893 6100 cell: +1 415 235 3778

This is my .sig. There are many like it, but this one is mine.

On Thu, Dec 18, 2003 at 02:11:20PM +0100, Kurt Roeckx wrote:

I find this a little strange:

select date_part('year', '0002-01-01 BC'::date);
date_part
-----------
-1

It seems 1 BC and 0 are the same 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);

It this normal or a bug?

I think this code is OK, butg is somethere in extract (date_part) code.

test=# select to_date('0020-01-10 BC'::text, 'YYYY-MM-DD BC');
to_date
---------------
0020-01-10 BC
(1 ��dka)

test=# select to_date('0020-01-10 AD'::text, 'YYYY-MM-DD BC');
to_date
------------
0020-01-10

test=# select to_char('0020-01-10 BC'::date, 'YYYY-MM-DD AD');
to_char
---------------
0020-01-10 BC

Karel
--
Karel Zak <zakkr@zf.jcu.cz>
http://home.zf.jcu.cz/~zakkr/

There is no zero calendar year. The first year of Anno Domini is 1. It's ordinal, not cardinal.

-----Original Message-----
From: Karel Zak [mailto:zakkr@zf.jcu.cz]
Sent: Friday, December 19, 2003 12:04 AM
To: Kurt Roeckx
Cc: pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] Dates BC.

On Thu, Dec 18, 2003 at 02:11:20PM +0100, Kurt Roeckx wrote:

I find this a little strange:

select date_part('year', '0002-01-01 BC'::date);
date_part
-----------
-1

It seems 1 BC and 0 are the same 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);

It this normal or a bug?

I think this code is OK, butg is somethere in extract
(date_part) code.

test=# select to_date('0020-01-10 BC'::text, 'YYYY-MM-DD BC');
to_date
---------------
0020-01-10 BC
(1 řádka)

test=# select to_date('0020-01-10 AD'::text, 'YYYY-MM-DD BC');
to_date
------------
0020-01-10

test=# select to_char('0020-01-10 BC'::date, 'YYYY-MM-DD AD');
to_char
---------------
0020-01-10 BC

Karel
--
Karel Zak <zakkr@zf.jcu.cz>
http://home.zf.jcu.cz/~zakkr/

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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

Karel

--
Karel Zak <zakkr@zf.jcu.cz>
http://home.zf.jcu.cz/~zakkr/

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
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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.

I have also add a doc mention to my patch that mentions that there is no
0 AD, and therefore subtraction of BC years from AD years must be done
with caution.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

On Mon, Mar 29, 2004 at 03:37:07PM -0500, Bruce Momjian wrote:

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.

I have also add a doc mention to my patch that mentions that there is no
0 AD, and therefore subtraction of BC years from AD years must be done
with caution.

The patch seems good for me. Thanks.

Karel

--
Karel Zak <zakkr@zf.jcu.cz>
http://home.zf.jcu.cz/~zakkr/

I have applied a patch to fix the issues mentioned below. Thanks.

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

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

Karel

--
Karel Zak <zakkr@zf.jcu.cz>
http://home.zf.jcu.cz/~zakkr/

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-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073