Getting number of days in a month

Here's my perl implementation:

#######################################
#
# lastday( month, year (4 digit) )
#
# Returns: last day of the month
#
#######################################

sub lastday {
my $month=shift;
my $year= shift;

$month--;

my @days = (31,0,31,30,31,30,31,31,30,31,30,31);

if($days[$month] != 0){
return $days[$month];
} else {
# It's Feb, test for leap year
if($year % 4 != 0){
return 28;
} elsif($year % 400 == 0){
return 29;
} elsif($year % 100 == 0){
return 28;
} else {
return 29;
}
}
}

Ken Causey
ineffable

At 02:26 PM 4/12/00 +0200, you wrote:

Ken Causey wrote:

Here's my perl implementation:

#######################################
#
# lastday( month, year (4 digit) )
#
# Returns: last day of the month
#
#######################################

sub lastday {
my $month=shift;
my $year= shift;

$month--;

my @days = (31,0,31,30,31,30,31,31,30,31,30,31);

if($days[$month] != 0){
return $days[$month];
} else {
# It's Feb, test for leap year
if($year % 4 != 0){
return 28;
} elsif($year % 400 == 0){
return 29;
} elsif($year % 100 == 0){
return 28;
} else {
return 29;
}
}
}

Ken Causey
ineffable

At 02:26 PM 4/12/00 +0200, you wrote:

To obtain the number of days in a month, I wrote this function:

CREATE FUNCTION dayCountOfMonth(datetime) RETURNS float AS
' DECLARE
theDate ALIAS FOR $1;
monthStart date;
monthEnd date;
BEGIN
monthStart := DATE_TRUNC(''month'', theDate);
monthEnd := monthStart + ''1 month''::timespan - ''1 day''::timespan;
RETURN DATE_PART(''doy'', monthEnd) - DATE_PART(''doy'', monthStart) + 1;
END;
' LANGUAGE 'PL/pgSQL';

It seems to work, except with the month of October (10).

dayCountOfMonth('1997-10-1') => 30
dayCountOfMonth('1998-10-1') => 30
dayCountOfMonth('1999-10-1') => 31
dayCountOfMonth('2000-10-1') => 30
dayCountOfMonth('2001-10-1') => 30
dayCountOfMonth('2002-10-1') => 30
dayCountOfMonth('2003-10-1') => 30
dayCountOfMonth('2004-10-1') => 31

Just one question: WHY??????
(Note: no trouble with February)

Is there a function that give the number of days of a month?

Thanks,

Guillaume Perr�al - Stagiaire MIAG
Cemagref (URH), Lyon, France
T�l: (+33) 4.72.20.87.64

Thanks, I rewrote my function to solve my problem.

In fact, the problem is that ('2000-10-01'::datetime + '1 month'::interval)
gives '2000-10-31' instead of '2000-11-01'.
I think it's a bug, isn't it?

Guillaume Perr�al - Stagiaire MIAG
Cemagref (URH), Lyon, France
T�l: (+33) 4.72.20.87.64

On Thu, Apr 13, 2000 at 09:24:36AM +0200, Guillaume Perr�al wrote:

Thanks, I rewrote my function to solve my problem.

In fact, the problem is that ('2000-10-01'::datetime + '1 month'::interval)
gives '2000-10-31' instead of '2000-11-01'.
I think it's a bug, isn't it?

It's our old friend daylight savings changeover:

rfb=# select ('2000-10-01'::datetime + '1 month'::interval);
?column?
------------------------
2000-10-31 23:00:00+00
(1 row)
^^

1 hour less because going from summer -> winter (For me BST->GMT)

Cheers,

Patrick

On Thu, Apr 13, 2000 at 10:26:17AM +0100, Patrick Welche wrote:

On Thu, Apr 13, 2000 at 09:24:36AM +0200, Guillaume Perr�al wrote:

Thanks, I rewrote my function to solve my problem.

In fact, the problem is that ('2000-10-01'::datetime + '1 month'::interval)
gives '2000-10-31' instead of '2000-11-01'.
I think it's a bug, isn't it?

It's our old friend daylight savings changeover:

rfb=# select ('2000-10-01'::datetime + '1 month'::interval);
?column?
------------------------
2000-10-31 23:00:00+00
(1 row)
^^

1 hour less because going from summer -> winter (For me BST->GMT)

Right - and it's 'fixable' by setting your timezone to GMT before doing the
math:

reedstrm=> set timezone to 'GMT';
SET VARIABLE
reedstrm=> select ('2000-10-01'::datetime + '1 month'::interval);
?column?
----------------------------
Wed Nov 01 00:00:00 2000 GMT
(1 row)

Hmm, now that I've said that, I discover that I can't set my timezone back
to the previous behavior: if I set the timezone to anything, it treats
all date values as being in that timezone, and the math just works,
even when I set it to 'unknown'. Hmm, I'll have to test 7.0beta5 for this.

Ross
--
Ross J. Reedstrom, Ph.D., <reedstrm@rice.edu>
NSBRI Research Scientist/Programmer
Computer and Information Technology Institute
Rice University, 6100 S. Main St., Houston, TX 77005