SQL, Updates,and Inserts

Question

Hey so i'm supposed to write a procedure AddSaleDetail that will add a sale detail for a book purchased and will update the sale with that book information. The data that needs to be passed in is sale number, ISBN and quantity. And i have to RaiseErrors for the following things which i have already done. The ISBN and sale numbers are not valid The ISBN is already on that sale.

And if there aren't any errors i have to insert the Sale Detail record into SaleDetail table. The selling price will be the Suggested Price for that ISBN.

Now everything i've got until the next two things that need to be done, this is where i'm unable to proceed.

Update the book in the Title table to reduce the number in stock by the quantity Update the Sale record subtotal, total and GST fields in Sale table to include the sale amount of the book purchased.

Here is what i have: ORIGINAL

Create Procedure AddSaleDetail
(
@salenumber int,
@ISBN char(10),
@Quantity int,
@NumberInStock smallint
)
AS

SELECT sale.saleNumber, title.ISBN, saledetail.quantity,NumberInStock
FROM   sale INNER JOIN
   saledetail ON sale.saleNumber = saledetail.saleNumber INNER JOIN
   title ON saledetail.ISBN = title.ISBN

IF @ISBN is null or @salenumber is null
BEGIN
RAISERROR ('Please enter valid ISBN and Sale Number',16,1) 
END

Else
BEGIN
declare @sellingprice money
select  @sellingprice= suggestedprice from title where ISBN=@ISBN
declare @amount money = @quantity * @sellingprice

If exists (select * from saledetail where ISBN=@ISBN)
BEGIN 
RAISERROR ('ISBN already exists',16,1)

END
ELSE 
    if not exists (select * from saledetail where saleNumber=@salenumber)
    BEGIN
    RAISERROR ('Sale Number Does not exist',16,1)
    END

        ELSE
        BEGIN
            INSERT INTO saledetail(ISBN,saleNumber, sellingprice)
            values (@ISBN,@salenumber,@sellingprice )           
        END
        END
            Else
            BEGIN
            Update title(NumberInStock =@NumberInStock - @Quantity where    ISBN=@ISBN)

Current

Create Procedure AddSaleDetail
(
@salenumber int,
@ISBN char(10),
@Quantity int,
@NumberInStock smallint
)
AS

SELECT sale.saleNumber, title.ISBN, saledetail.quantity,NumberInStock
FROM   sale INNER JOIN
   saledetail ON sale.saleNumber = saledetail.saleNumber INNER JOIN
   title ON saledetail.ISBN = title.ISBN

IF @ISBN is null or @salenumber is null
BEGIN
RAISERROR ('Please enter valid ISBN and Sale Number',16,1) 
END

Else
BEGIN
declare @sellingprice money
select  @sellingprice= suggestedprice from title where ISBN=@ISBN
declare @amount money = @quantity * @sellingprice

 If exists (select * from saledetail where ISBN=@ISBN)

BEGIN 
RAISERROR ('ISBN already exists',16,1)

END
ELSE 
    if not exists (select * from saledetail where saleNumber=@salenumber)
    BEGIN
    RAISERROR ('Sale Number Does not exist',16,1)
    END

    ELSE
        Begin Transaction
        BEGIN 
            INSERT INTO saledetail(ISBN,saleNumber, sellingprice)
            values (@ISBN,@salenumber,@sellingprice )   
            if @@Error<>0       
            Begin
            Raiserror ('insert failed',16,1)

            Rollback Transaction 
            END 

    Else
            Begin
            UPDATE Title
            SET NumberInStock = NumberInStock - @Quantity 
            WHERE ISBN = @ISBN
            if @@Error<>0
                Begin
                Raiserror('Update failed',16,1)
                Rollback Transaction
                End


    Else
            begin
            Commit Transaction
            END 
        END 
    END
END

Answer 1

How about this update:

UPDATE Title
SET NumberInStock = NumberInStock - @Quantity 
WHERE ISBN = @ISBN

The NumberInStock is a column, not a @ parameter.

Also, you can also do something like this, but you will have to create @total and @GST variables:

UPDATE Sale
SET subtotal = @amount,
total = @total,
GST = @GST
WHERE sale.saleNumber = @salenumber

I think your first SELECT query is not very useful. Your procedure will print out everything. But you already have the parameters you need, right? They are input parameters. I hope this helps?