IF (SELECT COUNT(*) FROM dbo.WarePrinterXtab (NOLOCK)) = 0 
  INSERT INTO dbo.WarePrinterXtab (WareNumber, PrinterNumber)
  SELECT WareNumber, P.PrinterNumber FROM dbo.Ware W (NOLOCK) 
    JOIN dbo.Printers P (NOLOCK) ON W.PrinterNumber = P.PrinterNumber
