create trigger
on tablename --将要保存的表
for inserted
begin
DECLARE @a1 as int,@b1 as int ,@c1 as int,@d1 as int,@pk as int

select TOP 1 @a1=A，@b1=B,@c1=C,@d1=D,@pk=id FROM INSERTED ---id为你保存到表里面的主键
if @b1=0 return;
else begin if (@b1<>0 AND @c1<>0)

                update tablename set    A=@b1*1000/@c1*@d1 where id=@pk
            end

end