Error handling in sql server

Syntax:

BEGIN TRY
     { Any set of SQL statements }
END TRY
BEGIN CATCH
     [ Optional: Any set of SQL statements ]
END CATCH
[Optional: Any other SQL Statements]

Error handling in sql server Syntax:

In procedure spSellProduct, Begin Transaction and Commit Transaction statements are wrapped between Begin Try and End Try block. If there are no errors in the code that is enclosed in the TRY block, then COMMIT TRANSACTION gets executed and the changes are made permanent. On the other hand, if there is an error, then the control immediately jumps to the CATCH block. In the CATCH block, we are rolling the transaction back. So, it’s much easier to handle errors with Try/Catch construct than with @@Error system function.

Create Procedure spSellProduct
@ProductId int,
@QuantityToSell int
as
Begin
 -- Check the stock available, for the product we want to sell
 Declare @StockAvailable int
 Select @StockAvailable = QtyAvailable 
 from tblProduct where ProductId = @ProductId
 
 -- Throw an error to the calling application, if enough stock is not available
 if(@StockAvailable < @QuantityToSell)
  Begin
  Raiserror('Not enough stock available',16,1)
  End
 -- If enough stock available
 Else
  Begin
   Begin Try
    Begin Transaction
        -- First reduce the quantity available
  Update tblProduct set QtyAvailable = (QtyAvailable - @QuantityToSell)
  where ProductId = @ProductId
  
  Declare @MaxProductSalesId int
  -- Calculate MAX ProductSalesId  
  Select @MaxProductSalesId = Case When 
          MAX(ProductSalesId) IS NULL 
          Then 0 else MAX(ProductSalesId) end 
         from tblProductSales
  --Increment @MaxProductSalesId by 1, so we don't get a primary key violation
  Set @MaxProductSalesId = @MaxProductSalesId + 1
  Insert into tblProductSales values(@MaxProductSalesId, @ProductId, @QuantityToSell)
    Commit Transaction
   End Try
   Begin Catch 
  Rollback Transaction
  Select 
   ERROR_NUMBER() as ErrorNumber,
   ERROR_MESSAGE() as ErrorMessage,
   ERROR_PROCEDURE() as ErrorProcedure,
   ERROR_STATE() as ErrorState,
   ERROR_SEVERITY() as ErrorSeverity,
   ERROR_LINE() as ErrorLine
   End Catch 
  End
End