This looks great and is a much easier solution to the problem than what I had planned.
Thanks! Keaton mydb=# select ( date('2009-01-01') + ('1 day'::interval * (21-1)*7)) - ('1 day'::interval * (select 7 - extract(dow from timestamp '2009-01-01'))); ?column? --------------------- 2009-05-18 00:00:00 (1 row) mydb=# select ( date('2009-01-01') + ('1 day'::interval * (21-1)*7)) - ('1 day'::interval * (select 7 - extract(dow from timestamp '2009-01-01'))) + '6 days'::interval; ?column? --------------------- 2009-05-24 00:00:00 (1 row) mydb=# select ( date('2009-01-01') + ('1 day'::interval * (22-1)*7)) - ('1 day'::interval * (select 7 - extract(dow from timestamp '2009-01-01'))); ?column? --------------------- 2009-05-25 00:00:00 (1 row) mydb=# select ( date('2009-01-01') + ('1 day'::interval * (22-1)*7)) - ('1 day'::interval * (select 7 - extract(dow from timestamp '2009-01-01'))) + '6 days'::interval; ?column? --------------------- 2009-05-31 00:00:00 (1 row) mydb=# select ( date('2009-01-01') + ('1 day'::interval * (1-1)*7)) - ('1 day'::interval * (select 7 - extract(dow from timestamp '2009-01-01'))); ?column? --------------------- 2008-12-29 00:00:00 (1 row) mydb=# select ( date('2009-01-01') + ('1 day'::interval * (1-1)*7)) - ('1 day'::interval * (select 7 - extract(dow from timestamp '2009-01-01'))) + '6 days'::interval; ?column? --------------------- 2009-01-04 00:00:00 (1 row) On 5/26/09 12:18 PM, "John R Pierce" <pie...@hogranch.com> wrote: > So for the calculated week value (i.e. 2009w22) I need to be able to > calculate the first and last day of the week (05/25/2009 and > 05/31/2009). Is there a clean / fairly easy way to do this? I can > think of doing some string comparisons and walking through date values > to figure it out but was wondering if there was a rather simplistic > way to do this that I am overlooking. well, a few things that come to mind..... figure out how many days are in the first partial week prior to week 1 of this year, that would be something like 7 - day_of_week(YYYY-01-01), then take '1 day'::interval * (week-1)*7 + that offset, and add that to YYYY-01-01 ... add '6 day'::interval to get the last day of the week...