Returning an existing column OR the scope_identity

[arichardson]

I'm having a seriously hard time trying to figure this one out.

I have a stored proc that must so one of the following:
based on a varchar value, if that value exists, return the rowID of it. If it does NOT exist, create a new row and return the new rowID

I have the following code and I have not been able to get it to work. I get the error ' Syntax error converting the varchar value 'XXX' to a column of data type int.' ( XXX is the @invoiceNumber value I'm supplying )

Could someone help me figure out what I'm doing wrong? :D

 [dbo].[CreateNewInvoice]
(
      @user varchar(50)
    , @invoiceNumber varchar(50)
)
 
AS
 
 
DECLARE @ID int;
 
        IF (( SELECT InventoryInvoiceNumber FROM InventoryInvoices WHERE InventoryInvoiceNumber = @invoiceNumber) > 0  )
        --return the existing id #
            BEGIN
                SELECT InventoryInvoiceID FROM InventoryInvoices WHERE InventoryInvoiceNumber = @invoiceNumber
            END
 
        ELSE
        --make an entry into the InventoryInvoice table first
            BEGIN
                INSERT INTO InventoryInvoices
                (
                      InventoryInvoiceNumber
                    , UserWhoEntered
                )
                VALUES
                (
                      @invoiceNumber
                    , @user
                )
                RETURN SCOPE_IDENTITY()
 
            END