Thread: date bug (again)
let me try this again...
Here is an other set of strange bugs I've discovered relating to dates.
this bug only rears it's head for 1 day a year form what I can find..
october 31'st, the intent of the queries is to get the last day of a month..
SELECT date_part('day', ('2000-11-1 0:00'::datetime + '-1day'))::int4 AS
days_in_month;
days_in_month
--------------
31
(1 row)
SELECT date_part('day', (('2000-10-1 0:00'::datetime + '1 month') + '-1
day'))::int4 AS days_in_month;
days_in_month
--------------
30
(1 row)
SELECT date_part('day', date_trunc('month', ('2000-10-1 0:00'::datetime +
'1 month')) + '-1 day')::int4 AS days_in_month;
days_in_month
--------------
30
(1 row)
At 22:38 14/08/00 -0700, Darcy Buskermolen wrote:
>let me try this again...
>
>
>Here is an other set of strange bugs I've discovered relating to dates.
>
>SELECT date_part('day', ('2000-11-1 0:00'::datetime + '-1day'))::int4 AS
>days_in_month;
>
> 31
>
>
>SELECT date_part('day', (('2000-10-1 0:00'::datetime + '1 month') + '-1
>day'))::int4 AS days_in_month;
>
> 30
>
>SELECT date_part('day', date_trunc('month', ('2000-10-1 0:00'::datetime +
>'1 month')) + '-1 day')::int4 AS days_in_month;
>
> 30
>(1 row)
FWIW, with 7.0.2 under Linux, I get 31 in each case.
----------------------------------------------------------------
Philip Warner | __---_____
Albatross Consulting Pty. Ltd. |----/ - \
(A.B.N. 75 008 659 498) | /(@) ______---_
Tel: (+61) 0500 83 82 81 | _________ \
Fax: (+61) 0500 83 82 82 | ___________ |
Http://www.rhyme.com.au | / \|
| --________--
PGP key available upon request, | /
and from pgp5.ai.mit.edu:11371 |/
this happens on FreeBSD 3.5-STABLE, running both 6.5.3 and 7.0.2
as well as FreeBSD 2.28-RELEASE running 6.4.(something)
At 03:52 PM 8/15/00 +1000, you wrote:
>At 22:38 14/08/00 -0700, Darcy Buskermolen wrote:
>>let me try this again...
>>
>>
>>Here is an other set of strange bugs I've discovered relating to dates.
>>
>>SELECT date_part('day', ('2000-11-1 0:00'::datetime + '-1day'))::int4 AS
>>days_in_month;
>>
>> 31
>>
>>
>>SELECT date_part('day', (('2000-10-1 0:00'::datetime + '1 month') + '-1
>>day'))::int4 AS days_in_month;
>>
>> 30
>>
>>SELECT date_part('day', date_trunc('month', ('2000-10-1 0:00'::datetime +
>>'1 month')) + '-1 day')::int4 AS days_in_month;
>>
>> 30
>>(1 row)
>
>FWIW, with 7.0.2 under Linux, I get 31 in each case.
>
>
>----------------------------------------------------------------
>Philip Warner | __---_____
>Albatross Consulting Pty. Ltd. |----/ - \
>(A.B.N. 75 008 659 498) | /(@) ______---_
>Tel: (+61) 0500 83 82 81 | _________ \
>Fax: (+61) 0500 83 82 82 | ___________ |
>Http://www.rhyme.com.au | / \|
> | --________--
>PGP key available upon request, | /
>and from pgp5.ai.mit.edu:11371 |/
>
>
Darcy Buskermolen <darcy@ok-connect.com> writes:
> SELECT date_part('day', (('2000-10-1 0:00'::datetime + '1 month') + '-1
> day'))::int4 AS days_in_month;
> days_in_month
> --------------
> 30
> (1 row)
This is not a bug, or at least it's not entirely clear what the behavior
ought to be. The issue is what happens at a daylight-savings
transition. The results I get (US Eastern timezone) are
regression=# select '2000-10-1 0:00'::timestamp;
?column?
------------------------
2000-10-01 00:00:00-04
(1 row)
regression=# select '2000-10-1 0:00'::timestamp + '1 month';
?column?
------------------------
2000-10-31 23:00:00-05
(1 row)
See what's happening? You get a result that's exactly 31 days times
24 hours later, but that date_trunc()'s down to only 30 days. A
finer-grain example is
regression=# select '2000-10-29 0:00'::timestamp ;
?column?
------------------------
2000-10-29 00:00:00-04
(1 row)
regression=# select '2000-10-29 0:00'::timestamp + '1 day';
?column?
------------------------
2000-10-29 23:00:00-05
(1 row)
The real question is whether "+ 1 day" ought to mean "+ 24 hours"
or not, and if not what it *should* mean...
regards, tom lane