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Re: BUG #6178: date_trunc : interval units "week" not supported contradicts documentation

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Noah Hamerslough <noah(at)pcc(dot)com>
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: BUG #6178: date_trunc : interval units "week" not supported contradicts documentation
Date: 2012-08-15 20:50:08
Message-ID: 20120815205008.GO25473@momjian.us (view raw or flat)
Thread:
Lists: pgsql-bugs
On Thu, Aug 25, 2011 at 07:05:34PM +0000, Noah Hamerslough wrote:
> 
> The following bug has been logged online:
> 
> Bug reference:      6178
> Logged by:          Noah Hamerslough
> Email address:      noah(at)pcc(dot)com
> PostgreSQL version: 8.4
> Operating system:   Windows Vista
> Description:        date_trunc : interval units "week" not supported
> contradicts documentation
> Details: 
> 
> http://www.postgresql.org/docs/8.4/static/functions-datetime.html#FUNCTIONS-
> DATETIME-TRUNC
> 
> The documentation for date_trunc('field', source) lists 'week' in the as a
> valid value for 'field' However, if the source is an interval, 'week' is not
> supported. 
> 
>  select date_trunc('week', '1 month 15 days'::interval);
> 
>  ERROR: interval units "week" not supported
>  SQL state: 0A000
> 
> Either 'week' should be supported or the documentation should be updated to
> reflect that it is not.

Turns out the reason we don't support this is because there are usually
a fractional number of weeks in a month, so there is no good way to do
this for intervals.   I have applied the attached patch to PG 9.3 which
will explain why this is not supported.  I saw this as better than a
documentation mention.

-- 
  Bruce Momjian  <bruce(at)momjian(dot)us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +

Attachment: week.diff
Description: text/x-diff (1.0 KB)

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