Updat mytab Set over_qty=case when over_qty<input_qty then 0 else over_qty-input_qty end
where...--(如果over_qty-input_qty小于0则为0,否则为over_qty-input_qty) where ....
where...--(如果over_qty-input_qty小于0则为0,否则为over_qty-input_qty) where ....
(case when over_qty<input_qty then 0 else over_qty-input_qty end)
where...
declare @input_qty int
Updat mytab Set
over_qty=case when over_qty<@input_qty then 0 else over_qty-input_qty end
where 條件
Set over_qty =(case when over_qty-input_qty<0 then 0 else over_qty-input_qty end)
where ....
Set over_qty =(case when over_qty-input_qty>0 then over_qty-input_qty else 0 end)
where ....
@input_qty decimal(10, 4)
as
declare @Over_qty decimal(10, 4)
select @Over_qty = Over_qty from mytab
if @input_qty < @Over_qty
-- begin
set @input_qty = 0
-- end
else
set @input_qty= @input_qty - @Over_qty