DECLARE kalender VARCHAR(5);
 
	(...)
 
	DECLARE C1 CURSOR FOR
		SELECT min(datum) min, max(datum) max 
 		FROM bibliothek.kalender
		WHERE week_iso(datum) = w
 		AND year(datum) = y
 		AND kalender <> '0';

CASE
WHEN kal = '1' THEN 
	SET kalender = 'kal1';
WHEN kal = '2' THEN
	SET kalender = 'kal2';
WHEN kal = '3' THEN
	SET kalender = 'kal3';
END CASE;