Function overlaps_interval

Folks,

I wrote this PL/pgSQL function for my current project, and thought it
would be generally useful. An expansion of the builtin
overlaps(dt1,dt2,dt3,dt4) function, this function returns the interval
of time for which the two datetime ranges overlap.

Roberto, please include this in your online PL/pgSQL function library.

CREATE FUNCTION overlap_interval(DATETIME, DATETIME, DATETIME, DATETIME)
RETURNS INTERVAL AS '
DECLARE
begin1 ALIAS for $1;
end1 ALIAS for $2;
begin2 ALIAS for $3;
end2 ALIAS for $4;
overlap_amount INTERVAL;
BEGIN
--test for overlap using the ovelap function.
--if not found, return 0 interval.

IF NOT overlaps(begin1, end1, begin2, end2) THEN
RETURN ''00:00:00''::INTERVAL;
END IF;

--otherwise, test for the various forms of overlap

IF begin1 < begin2 THEN
IF end1 < end2 THEN
overlap_amount := end1 - begin2;
ELSE
overlap_amount := end2 - begin2;
END IF;
ELSE
IF end1 < end2 THEN
overlap_amount := end1 - begin1;
ELSE
overlap_amount := end2 - begin1;
END IF;
END IF;

RETURN overlap_amount;
END;'
LANGUAGE 'plpgsql';

-Josh Berkus

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