How can I fix this error with SQL server query

Question

I'm having an error when I try to execute this query.

This is the error (Msg 156, Level 15, State 1, Procedure SP_GetAllProducts, Line 43 Incorrect syntax near the keyword 'as'.)

and these are my query codes

create procedure [dbo].[SP_GetAllProducts] (@CategoryID INT)
as
    begin
        begin try
            if(@CategoryID <> 0)
                begin
                    select * 
                    from (select P.CategoryID,
                                 P.ProductID,
                                 P.Name,
                                 P.Price,
                                 P.ImageUrl,
                                 C.CategoryName,
                                 P.ProductQuantity,
                                 Isnull(Sum(CP.TotalProduct), 0)                        as ProductSold,
                                 (P.ProductQuantity - Isnull(Sum(CP.TotalProduct), 0) ) as AvailableStock
                            from Products P
                                inner join Category C
                                            on C.CategoryID = P.CategoryID
                                left join       CustomerProducts CP
                                            on CP.ProductID = P.ProductID
                            group by P.ProductID,
                                     P.Name,
                                     P.Price,
                                     P.ImageUrl,
                                     C.CategoryName,
                                     P.ProductQuantity,
                                     P.CategoryID) StockTable
                            where AvailableStock > 0
                                and CategoryID = @CategoryID
                end
            else
                begin
                    select * 
                    from (select P.CategoryID,
                                 P.ProductID,
                                 P.Name,
                                 P.Price,
                                 P.ImageUrl,
                                 C.CategoryName,
                                 P.ProductQuantity,
                                 Isnull(Sum(CP.TotalProduct), 0)                        as ProductSold,
                                 (P.ProductQuantity - Isnull(Sum(CP.TotalProduct), 0)   as AvailableStock
                            from Products P
                                inner join Category C
                                        on C.CategoryID = P.CategoryID
                                left join CustomerProducts CP
                                        on CP.ProductID = P.ProductID
                            group by P.ProductID,
                                     P.Name,
                                     P.Price,
                                     P.ImageUrl,
                                     C.CategoryName,
                                     P.ProductQuantity,
                                     P.CategoryID) StockTable
                            where AvailableStock > 0
                end
            end try

            begin catch
                print('Error occurd')
            end catch
    end

Answer 1

You are missing a closing bracket, see the same line in the IF block, it has three closing brackets whereas the else part has only two!

(P.ProductQuantity - Isnull(Sum(CP.TotalProduct), 0) ) ) as AvailableStock