Re: Obtaining the Julian Day from a date

"Karl O. Pinc" <kop@meme.com> writes:
> On 2004.09.10 20:32 Bruno Wolff III wrote:
>> If you keep your data in a date field you can get the Julian day
>> by subtracting the appropiate date. You can then do mod on this
>> difference.

> I've been doing:
> CAST (to_char(date, 'J') AS INT)
> but your way seems faster.  Is it?

Date subtraction is extremely fast (it's really the same as integer
subtraction), so yes I'd expect it to beat the pants off doing to_char
and then conversion back to integer.

Another advantage is that you can equally easily adopt *any* base date,
it doesn't have to be Julian day 0.  This would let you shift between
say Monday and Sunday as start-of-the-week without extra logic.

            regards, tom lane