Message-ID: <3E817B63.2040006@klaster.net>
Date: Wed, 26 Mar 2003 11:05:23 +0100
From: Tomasz Myrta <jasiek@klaster.net>
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To: Peter Childs <blue.dragon@blueyonder.co.uk>
Cc: pgsql-sql@postgresql.org
Subject: Re: Does anyone use TO_CHAR(INTERVAL)?
References: <Pine.LNX.4.44.0303260929090.5091-100000@RedDragon.Childs>
In-Reply-To: <Pine.LNX.4.44.0303260929090.5091-100000@RedDragon.Childs>
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Uz.ytkownik Peter Childs napisa?:
> On Wed, 26 Mar 2003, Tomasz Myrta wrote:
>=20
>=20
>>Thanks for noticing this, these results are really strange for me.
>>I should remember NOT to use months when working with intervals. It=20
>>looks like intervals contain 2 totally independent values inside.
>>
>>I have one more question to this thread - Does anyone use intervals=20
>>month value?
>=20
>=20
> 	Since all months are not equal in length how do else do you come=20
> up with an interval that is 1 month since us humans like to use months.
> 	As you note Postgres trys to ovide using Months if at all possible=20
> because 1 month <> 1 month hense.
>=20
> select (cast('2-2-2003' as date) + cast('1 month' as interval)) -=20
> cast('2-2-2003' as date);
>  ?column?
> ----------
>  28 days
> (1 row)
>=20
> but if all you say is 1 month from now how many days you month you mean=
=20
> will mean a different number of days. Oh one more good one is....
>=20
> select cast('1 year' as interval) - cast('365 days' as interval);
>      ?column?
> ------------------
>  1 year -365 days
> (1 row)
>=20
> 	It would seam that a year is 12 months but not 365 days which=20
> while this is true (due to leap years) most people would never think like=
=20
> that. Its seams that postgres will not tell you how many days there are i=
n=20
> a year but this seams even more stupid=20
>=20
> select cast('1 month' as interval)/2 * 2;
>  ?column?
> ----------
>  360 days
> (1 row)
>=20
> oh and just when you thought somthing was really straght forward you=20
> get...
>=20
> select cast('1 year' as interval)/24 * 24;
>  ?column?
> ----------
>  360 days
> (1 row)
>=20
> 	This reminds me of a calculator that comes with MS Windows....
> 	How ever the implementation in postgres is the best I've sean so=20
> long as you don't do anything stupid!
>=20
> Peter Childs

I already know all of these things (look at thread "Formatting=20
intervals" dated on 2003-03-17). I was just thinking about intervals=20
idea. Keeping time inside interval is good. Keeping months inside=20
interval also looks good, but keeping both of them doesn't make sense.=20
It is impossible to use these fields together without referring them to=20
some real date.

Tomasz Myrta