Oracle 批量更新

Question

麻烦大家帮我看一下这个sql语句为什么不对。
update 
(select stom.qty qty ,std.stocktaking_qty  stocktaking_qty
from stocktaking_master stm,stocktaking_detail std ,storage_master stom
          where stm.stocktaking_no = '10000000000001 ' and std.stocktaking_no = stm.stocktaking_no 
              and stom.warehouse_no = stm.warehouse_no and stom.product_no = std.product_no and 
              stom.lot_no = std.lot_no
           )
           set qty = stocktaking_qty

Answer 1

update storage_master stom
   set qty = (select std.stocktaking_qty
                from stocktaking_master stm, stocktaking_detail std
               where stm.stocktaking_no = '10000000000001 '
                 and std.stocktaking_no = stm.stocktaking_no
                 and stom.warehouse_no = stm.warehouse_no
                 and stom.product_no = std.product_no
                 and stom.lot_no = std.lot_no
                 and rownum < 2)

Answer 2

update storage_master stom
   set qty = (select std.stocktaking_qty
                from stocktaking_master stm, stocktaking_detail std
               where stm.stocktaking_no = '10000000000001 '
                 and std.stocktaking_no = stm.stocktaking_no
                 and stom.warehouse_no = stm.warehouse_no
                 and stom.product_no = std.product_no
                 and stom.lot_no = std.lot_no
                 and rownum < 2)
 where exists (select 1
          from stocktaking_master stm, stocktaking_detail std
         where stm.stocktaking_no = '10000000000001 '
           and std.stocktaking_no = stm.stocktaking_no
           and stom.warehouse_no = stm.warehouse_no
           and stom.product_no = std.product_no
           and stom.lot_no = std.lot_no)