oracle 分页

oracle分页：21 40  在java里面根据页数及每页显示条数计算

                       SELECT * FROM 
			(
				SELECT A.*, ROWNUM RN 
				FROM (SELECT * FROM TABLE_NAME) A 
				WHERE ROWNUM <= 40
			)
			WHERE RN >= 21

注意：不能够直接 rownum<=40 and >=21 这样写