Date: Wed, 6 Sep 2023 16:53:15 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Laurenz Albe <laurenz.albe@cybertec.at>
Cc: barsikdacat@gmail.com, pgsql-docs@lists.postgresql.org
Subject: Re: to_char(numeric type, text) rounding instead of truncating
Message-ID: <ZPjmu9EEMOcfkVsv@momjian.us>
References: <168991536429.626.9957835774751337210@wrigleys.postgresql.org>
 <bab04d8c091629a3f17d476af5eda6982d7e0e0d.camel@cybertec.at>
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On Wed, Jul 26, 2023 at 07:53:36AM +0200, Laurenz Albe wrote:
> On Fri, 2023-07-21 at 04:56 +0000, PG Doc comments form wrote:
> > The following documentation comment has been logged on the website:
> > 
> > Page: https://www.postgresql.org/docs/15/functions-formatting.html
> > Description:
> > 
> > I've encountered an issue with to_char(numeric type, text)
> > Apparently, it uses rounding instead of truncation which leads to
> > unpexpected results. This is not reflected in the documentation.
> > My specific example:
> > select to_Char(1235::real/(2::real+1235::real)*100, '99%')
> > The expected output was 99%. The output was ##% - since the number was
> > rounded to 100, there wasn't enough digits in the format.
> > If I add a digit after the decimal point
> > select to_char(1235::real/(2::real+1235::real)*100,'90D0%')
> > The output becomes 99.8%
> > 
> > It would be nice to have this behavior explained in the documentation so
> > people get more predictable results.
> 
> +1
> 
> How about the following:

I slightly modified your patch and applied it back to PG 11 since all
supported Postgres versions have the same behavior.  Thanks.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

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