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.