From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | "Milen A(dot) Radev" <milen(at)radev(dot)net> |
Cc: | pgsql-sql(at)postgresql(dot)org, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: [SQL] Interval subtracting |
Date: | 2006-02-18 18:30:14 |
Message-ID: | 20402.1140287414@sss.pgh.pa.us |
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"Milen A. Radev" <milen(at)radev(dot)net> writes:
> Milorad Poluga :
>>> SELECT '10 years 1 mons 1 days'::interval - '9 years 10 mons 15 days'::interval
>>> ?column?
>>> ---------------
>>> 3 mons -14 days
>>>
>>> Why not '2 mons 16 days' ?
> Please read the last paragraph in section 8.5.1.4 of the manual
> (http://www.postgresql.org/docs/8.1/static/datatype-datetime.html#AEN4775)
> . It mentions the functions named "justify_days" and "justify_hours"
> that could do what you need.
justify_days doesn't currently do anything with this result --- it
thinks its charter is only to reduce day components that are >= 30 days.
However, I think a good case could be made that it should normalize
negative days too; that is, the invariant on its result should be
0 <= days < 30, not merely days < 30. Similarly for justify_hours.
Comments anyone? Patch anyone?
regards, tom lane
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