On Jun 4, 2007, at 10:27 , Andrew Sullivan wrote:
On Mon, Jun 04, 2007 at 10:04:37AM -0500, Joshua wrote:
that will return the date of the first Monday of the month?
I guess you need to write a function to do this. I suppose you could
do it by finding out what day of the week it is and what the date is,
then counting backwards to the earliest possible Monday.
As Andrew said, there's no built-in function to do this, but it's
easy enough to write one. Here's a rough example (very lightly tested
and probably overly complicated)
CREATE OR REPLACE FUNCTION first_dow(DATE, INTEGER)
RETURNS DATE
IMMUTABLE
LANGUAGE SQL AS $_$
SELECT v_first_day_of_month +
CASE WHEN v_day_of_week <= $2 THEN $2 - v_day_of_week
ELSE 8 - v_day_of_week
END AS first_day_of_month
FROM (
SELECT v_first_day_of_month
, extract('dow' from v_first_day_of_month)::integer
AS v_day_of_week
FROM (SELECT date_trunc('month', $1)::date)
AS mon(v_first_day_of_month)) as calc;
$_$;
CREATE OR REPLACE FUNCTION first_monday(DATE)
RETURNS DATE
IMMUTABLE
LANGUAGE SQL AS $_$
SELECT first_dow($1, 1);
$_$;
select first_monday(current_date);
first_monday
--------------
2007-06-04
(1 row)
select first_monday('2007-04-01');
first_monday
--------------
2007-04-02
(1 row)
Michael Glaesemann
grzm seespotcode net
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