create trigger alter_table on table stock
for insert
as 
declare @productname varchar(50)
declare @Companyname varchar(50)
declare @number int 
declare @type varchar(50)
declare @sql varchar(4000)
declare c_cur cursor
for select productname,Companyname,Number,Type from inserted
open c_cur
fetch next from c_cur into @productname,@Companyname,@number,@type
while @@fetch_status=0 
begin
    if not exists( select * from Total where productname=@productname and Companyname=@Companyname)
    begin
       insert into Total(productname,Companyname) values(@productname,@Companyname)
    end 
    update Total 
    set Stocknumber=(case when @type='进货信息' then @number else 0 end),
    set Stock_back=(case when @type='进货退货信息' then @number else 0 end),
    set Sellnumber=(case when @type='销售信息' then @number else 0 end),
    set Sell_back=(case when @type='销售退货信息' then @number else 0 end) 
    where productname=@productname and Companyname=@Companyname)
fetch next from c_cur into @productname,@Companyname,@number,@type
end
close c_cur
deallocate c_cur