how to update in storeprocedure

Question

USE [Agri]

GO

/****** Object:  StoredProcedure [dbo].[in_dm]    Script Date: 09/14/2013 11:16:44 ******/

SET ANSI_NULLS ON

GO

SET QUOTED_IDENTIFIER ON

GO

create PROCEDURE [dbo].[idm]

(@Product varchar(15),@Date DateTime ,@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 varchar(50),

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

)

AS

BEGIN

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

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

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

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

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

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

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

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

@Vat,@CorrectPrice,@type );

END

if @type='s'

begin

update pr set purno=purno-Requiredno where BrandName=@BrandName

end

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need to update the table  pr reduce the requiredno from purno (but requiredno is not inn the table pr) the required no is in the table sampl and samle .