--2000
select * from
(
select * , px = (select count(1) from tb where [item num] < t.[item num] or ([item num] = t.[item num] and item < item)) + 1 from tb t
) t
where (px - 1)/2000
--2005用row_number
select * from
(
select * , px = row_number() from tb t
) t
where (px - 1)/2000