update a set @qty = c.nowqty,     @newqty = b.totalqty - @qty,     a.nowquantity = (case when @newqty<=0 then @qty-b.totalqty                           when @newqty>0                              and a.id = (select top 1 id from #stockte where a.warehouseid = warehouseid                                              and a.cinvcode = cinvcode and a.color = color and flag = 2                                             and a.[size] = [size] order by id desc)                             and not exists (select 1 from IM_StockRecord where a.warehouseid = warehouseid                                              and a.cinvcode = cinvcode and a.color = color and recordtype = 1                                             and a.[size] = [size] and nowquantity < 0)                             then @qty-b.totalqty else 404 end) from IM_stockRecord a join #stockte b on a.id = b.id     join crt c on a.id = c.id where b.flag = 2

a.id = (select top 1 id from #stockte where a.warehouseid = warehouseid                                              and a.cinvcode = cinvcode and a.color = color and flag = 2                                             and a.[size] = [size] order by id desc)

update a
set @qty = c.nowqty,
    @newqty = b.totalqty - @qty,
    a.nowquantity = (case when @newqty<=0 then @qty-b.totalqty
                          when @newqty>0 
                            and d.id is not null
                            and not exists (select 1 from IM_StockRecord where a.warehouseid = warehouseid 
                                            and a.cinvcode = cinvcode and a.color = color and recordtype = 1
                                            and a.[size] = [size] and nowquantity < 0)
                            then @qty-b.totalqty else 404 end)
from IM_stockRecord a 
join #stockte b on a.id = b.id
join crt c on a.id = c.id
outer apply
(select id from #stockte where a.warehouseid = warehouseid 
 and a.cinvcode = cinvcode and a.color = color and flag = 2
 and a.[size] = [size] and a.id=id) d
where b.flag = 2

------解决方案--------------------
SQL code

from IM_stockRecord a join #stockte b on a.id = b.id
    join crt c on a.id = c.id

------解决方案--------------------
top 1 的字段值是null呗。

------解决方案--------------------
我一般都是直接先select然后再对数据进行操作，方便分析．

select  
   e.nowquantity = (case ...then @qty-b.totalqty else 404 end)
from IM_stockRecord e join #stockte b on e.id = b.id
   join crt c on e.id = c.id
where b.flag = 2