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Re: [BUGS] BUG #14632: Plus and minus operators inconsistency withleap years and year intervals. - Mailing list pgsql-bugs

From Marko Tiikkaja
Subject Re: [BUGS] BUG #14632: Plus and minus operators inconsistency withleap years and year intervals.
Date
Msg-id CAL9smLA-=kOGepqaWhv+C7qsWQkL92nn5rmXHuNC4aRp5-4skA@mail.gmail.com
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In response to [BUGS] BUG #14632: Plus and minus operators inconsistency with leap yearsand year intervals.  (pietro.pugni@gmail.com)
Responses Re: [BUGS] BUG #14632: Plus and minus operators inconsistency withleap years and year intervals.
Re: [BUGS] BUG #14632: Plus and minus operators inconsistency withleap years and year intervals.
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On Wed, Apr 26, 2017 at 8:23 PM, <pietro.pugni@gmail.com> wrote:
The following bug has been logged on the website:

Bug reference:      14632
Logged by:          Pietro Pugni
Email address:      pietro.pugni@gmail.com
PostgreSQL version: 9.6.2
Operating system:   Ubuntu 16.04.2 LTS
Description:

The following query:
 SELECT '1912-02-29'::date + '10 years'::interval

returns:
 '1922-02-28 00:00:00'

while the reverse operation:
 SELECT '1922-02-28'::date - '10 years'::interval

returns:
 '1912-02-28 00:00:00'

instead of '1912-02-29 00:00:00'.

And if you change that, then this happens:

   SELECT date '1912-02-28' + interval '10 years' - interval '10 years';
      ?column?      
---------------------
 1912-02-29 00:00:00
(1 row)

which is obviously not correct either.

The problem is that after the subtraction the date '1912-02-28' doesn't know it's supposed to be the last date of the month instead of the 28th, specifically.  And you can't really fix that without breaking pg_upgrade and probably hundreds of applications using the binary format for dates.

You'll just have to take this into account when working on your application.


.m

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