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

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@pcc.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@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

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