date_part patch

Attached is small patch that extends the date_part function to return the
day of week and day of year respectively.

Two new tokens are introduced, weekday and yearday to allow
for the retrieval of the day number since sunday (0-6) or the day
number since january, 1 from a date value.

I use it to retrieve events on specific weekdays, e.g. all events
that occur on mondays:

SELECT * FROM events WHERE date_part('weekday', eventdate) = 1;

The following files are patched:

src/backend/utils/adt/datetime.c:
Extends "units" table to recognize the new tokens

src/backend/utils/adt/timestamp.c:
Extends timestamp2tm() function to return the fields tm_mday and tm_yday
Extends timestamp_part() function to return the day of week or day of year

src/include/utils/datetime.h:
Defines new tokens DTK_WEEKDAY, DTK_YEARDAY

<Der Anhang fehlt>
--
Marc Balmer, Micro Systems, Kannenfeldstrasse 32, CH-4056 Basel
Tel +41 61 383 05 10, Fax +41 61 383 05 12, http://www.msys.ch/