how to reduce in sqlserver

Question

USE [Agri]

GO

/****** Object:  StoredProcedure [dbo].[inse_sales]    Script Date: 09/21/2013 12:44:58 ******/

SET ANSI_NULLS ON

GO

SET QUOTED_IDENTIFIER ON

GO

ALTER PROCEDURE [dbo].[inse_sales]

(@ProductName varchar(15),@Date varchar(20) ,@BillNo varchar(30) ,

@CustomerName varchar(50),@Address varchar(50) ,

@BrandName varchar(50) ,@Quantity varchar(20),

@ProductPrice varchar(20) ,@Requiredno varchar(50),

@Price varchar(50),@Extra varchar(20) ,

@Vat varchar(50),@TotalAmount float,

@CorrectPrice varchar(50),@type varchar(10)

)

AS

BEGIN

insert into orgnal (ProductName,Date,BillNo,CustomerName,Address,BrandName,

Quantity,ProductPrice,Requiredno,Price,Vat,TotalAmount,type)

values(@ProductName,@Date,@BillNo ,@CustomerName ,@Address ,@BrandName ,

@Quantity ,@ProductPrice ,@Requiredno ,@Price ,@Vat ,@TotalAmount,@type);

insert into dummy (ProductName,Date,BillNo,CustomerName,Address,BrandName,

Quantity,ProductPrice,Requiredno,Price,Extra,Vat,CorrectPrice) values 

(@ProductName ,@Date,@BillNo ,@CustomerName ,@Address ,@BrandName ,@Quantity ,

@ProductPrice ,@Requiredno ,@Price ,@Extra ,

@Vat,@CorrectPrice );

if @type='s'

begin

declare @puno int

set @puno=(select purno from purchaseprodu where brandname in ('ProductName','ProductPrice'))

declare @Reqno int

set @Reqno=(select @Requiredno from orgnal where brandname in ('ProductName','ProductPrice'))

declare @ans int

set @ans=@puno-@Reqno

update purchaseprodu set purno=ISNULL(@puno,0)-ISNULL(@Reqno,0) where  brandname in ('ProductName','Price')

end

END

command executed but  purno is not reduced...