Message-ID: <4A49B5EE.8030309@megafon.hr>
Date: Tue, 30 Jun 2009 08:51:26 +0200
From: Mario Splivalo <mario.splivalo@megafon.hr>
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To: Tom Lane <tgl@sss.pgh.pa.us>
CC: pgsql <pgsql-sql@postgresql.org>
Subject: Re: date_trunc should be called date_round?
References: <4A487F94.3070303@megafon.hr> <11724.1246285520@sss.pgh.pa.us>
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Tom Lane wrote:
> Mario Splivalo <mario.splivalo@megafon.hr> writes:
>> But, date_trunc behaves like round function: round(1.9) = 2.
> 
> Hmm ... only for float timestamps, and only for the millisec/microsec
> cases.
> 
>             case DTK_MILLISEC:
> #ifdef HAVE_INT64_TIMESTAMP
>                 fsec = (fsec / 1000) * 1000;
> #else
>                 fsec = rint(fsec * 1000) / 1000;
> #endif
>                 break;
>             case DTK_MICROSEC:
> #ifndef HAVE_INT64_TIMESTAMP
>                 fsec = rint(fsec * 1000000) / 1000000;
> #endif
>                 break;
> 
> I wonder if we should change this to use floor() instead.
> 

I guess it's safe, since you don't have negative timestamps (right?) or
parts of timestamps (millisecs/microsecs), so floor() would act as trunc.

Esp. if for the other parts of timestamp (days, hours, ...) it's actualy
truncating, not rounding, i.e.:

date_trunc('minute', '2009-01-01 12:13:50'::timestamp)

would return '2009-01-01 13:13:00', not '2009-01-01 13:14:00'.

One would expect similar behavior for the milli/microsec part.

Now it's truncating, unless dealing with milli/microseconds, where it's
rounding.

	Mike