Обсуждение: Creating a selective aggregate ??

"Najib Abi Fadel" <nabifadel@usj.edu.lb> writes:

> Any ideas??
> Could this be done with aggregates ??

I think you're going to have to write code that reads all the records, keeps
state representing the current period start and the last seen end date and
outputs data every time it sees a gap like you want.

This could be a set returning plpgsql or plperl or plwhatever function, but it
may be easier to write it in your application level code.

-- 
greg

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> I am searching for a way to have the minimum date and maximum
> date for dates seperated by one week whitout gaps between them.
This is not something you can accomplish (easily) with just SQL,
so you will need some sort of higher language. Here's a little
function I came up with, which might do what you want:
CREATE OR REPLACE FUNCTION noweekgaps() RETURNS SETOF TEXT AS '
DECLARE startday TEXT; endday TEXT; lastone INT; mydiff INT; myrec RECORD;
BEGIN 
FOR myrec IN SELECT TO_CHAR(d, \'Mon DD, YYYY\') AS z,   TO_CHAR(d,\'J\')::integer AS j FROM t ORDER BY d ASC LOOP IF
startdayIS NULL THEN   startday := myrec.z; ELSE   mydiff := myrec.j - lastone;   IF mydiff > 7 THEN     RETURN NEXT
startday|| \' - \' || endday;     startday := myrec.z;   END IF; END IF; lastone := myrec.j; endday := myrec.z;
 
END LOOP; 
IF endday IS NOT NULL THEN RETURN NEXT startday || \' - \' || endday;
END IF; 
RETURN;
END;
' LANGUAGE plpgsql;
- --
Greg Sabino Mullane greg@turnstep.com
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