The query could be simplified if you're only interested in skipped series between min and max values in the table

SELECT t1.Orno+1 AS bg, t2.Orno-1 AS en
	FROM #mytable t1 
	FULL JOIN #mytable t2 
		ON t2.Orno > t1.Orno
	WHERE (t2.Orno - t1.Orno) > 1
		AND NOT EXISTS ( SELECT * FROM #mytable 
			WHERE Orno > t1.Orno AND Orno < t2.Orno)

>
>Thanks for the reply. I Will try what you suggested and will keep you posted.