--q21.sql--

 select * from(
   select w_warehouse_name, i_item_id,
          sum(case when (cast(d_date as date) < cast ('2000-03-11' as date))
	                  then inv_quantity_on_hand
                   else 0 end) as inv_before,
          sum(case when (cast(d_date as date) >= cast ('2000-03-11' as date))
                   then inv_quantity_on_hand
                   else 0 end) as inv_after
   from inventory, warehouse, item, date_dim
   where i_current_price between 0.99 and 1.49
     and i_item_sk          = inv_item_sk
     and inv_warehouse_sk   = w_warehouse_sk
     and inv_date_sk        = d_date_sk
     and d_date between (cast('2000-03-11' as date) - interval '30' day)
                    and (cast('2000-03-11' as date) + interval '30' day)
   group by w_warehouse_name, i_item_id) x
 where (case when inv_before > 0
             then inv_after / inv_before
             else null
             end) between 2.0/3.0 and 3.0/2.0
 order by w_warehouse_name, i_item_id
 limit 100