Re: [SQL] Interval subtracting

Tom Lane wrote:
> "Milen A. Radev" <milen@radev.net> writes:
> 
>>Milorad Poluga напи�а:
>>
>>>>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?

Sure, if nobody objects to this change I can write the patch.

mark