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Re: Date_part & cast.

From: Christopher Sawtell <csawtell(at)xtra(dot)co(dot)nz>
To: Benoit Brodard <benoit(at)cyberdeck(dot)net>, pgsql-sql(at)postgresql(dot)org
Subject: Re: Date_part & cast.
Date: 2000-04-21 23:48:40
Message-ID: 00042212582300.29813@berty (view raw or flat)
Thread:
Lists: pgsql-sql
On Fri, 21 Apr 2000, Benoit Brodard wrote:
> Hi,
> 
> We use PostgreSQL 6.5.3 on i586-pc-linux-gnu, compiled by gcc 2.7.2.3, and we get the following results with date_part :
> 
> db=> select date_part( 'dow', date '20000421' );
> date_part
> ---------
>         5
> (1 row)
> 
> db=> select date_part( 'dow', date ( '20000421' ) );
> date_part
> ---------
>         6
> (1 row)
> 
> Is this correct ?
No it is not.

> If yes, I could not find any explanation for the second result which also
> differ from "select date_part( 'dow', date (20000421)  );"

This, together with "hundreds" of other problems, has been fixed in
postgresql-7.0RC1. 

btw, the days of the week start with Sunday = 1

so your queries now say:-

template1=# select date_part( 'dow', date '20000421' );
 date_part
-----------
         6
(1 row)
 
template1=# select date_part( 'dow', date ( '20000421' ) );
 date_part
-----------
         6
(1 row)

However I think this demonstrates a bug in the date functions.

chris(at)berty:~ >  cal 11 1927       # In which I trust.
    November 1927
Su Mo Tu We Th Fr Sa
       1  2  3  4  5
 6  7  8  9 10 11 12
13 14 15 16 17 18 19
20 21 22 23 24 25 26
27 28 29 30

template1=# select date_part( 'dow', date '19271124' );
 date_part
-----------
         4
(1 row)
              
template1=# select date_part( 'dow', date '19271125' );
 date_part
-----------
         5
(1 row)
 
template1=# select date_part( 'dow', date '19271126' );
 date_part
-----------
         0
(1 row)         

template1=# select date_part( 'dow', date '19271127' );
 date_part
-----------
         1
(1 row)
                                                                                  
There seems to be a discontinuity here doesn't there?

Using postgresql-7.0RC1.

If somebody could direct me to the general area in the source tree, I might be
able to come up with a patch & btw, to whom should I send it?

-- 
Sincerely etc.,

 NAME       Christopher Sawtell - iOpen Technologies Ltd.
 CELL PHONE 021 257 4451
 ICQ UIN    45863470
 EMAIL      chris @ iopen . co . nz,  csawtell @ xtra . co . nz
 WWW        http://www.iopen.co.nz
 CNOTES     ftp://ftp.funet.fi/pub/languages/C/tutorials/sawtell_C.tar.gz

 -->> Please refrain from using HTML or WORD attachments in e-mails to me <<--


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