Re: Interval subtracting

Milorad Poluga написа:
> On Saturday 18 February 2006 15:24, Milen A. Radev wrote:
>> Milorad Poluga написа:
>>> Hi all,
>>>
>>> Is there something incorrect in the above query ? 
>>> 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' ? 
>>>
>>> /version =  PostgreSQL 8.0.4 on i686-pc-linux-gnu, compiled by GCC gcc (GCC) 3.4.2 20041017 (Red Hat 3.4.2-6.fc3)
/
>>
>> How many days are there in a month?
>>
> 
> I beleive that a month is calculated on the 30-days base.

Are you sure? Where?

> 
> One way to solve this problem is to use a neutal date element and make timestamps :
> 
> SELECT age(('1990-01-01'::date + '10 years 1 mons 1 days'::interval)::timestamp ,
>      ('1990-01-01'::date + '9 years 10 mons 15 days'::interval)::timestamp)
> 
>  age            
>  -------------- 
>  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.


-- 
Milen A. Radev