我需要内部联接3个表的帮助

Question

我尝试加入3张桌子

@Service
public class ShippingService {
     @Autowired
     private ShippingMethodRespository shippingMethodRespository;

     public ModelAndView saveShippingMethod(HttpServletRequest request, String id) {
        Shipping shipping=new Shipping();
        shipping.setName(request.getParameter("name"));
        shippingMethodRespository.save(shipping);
        ModelAndView shippingMethodsPage = new 
        ModelAndView("/Shipping/ShippingMethodList");
        return shippingMethodsPage;
    }    
}

  

警告：mysqli_fetch_assoc（）期望参数1为mysqli_result，   在第15行的C：\ xampp \ htdocs \ udemy-cms \ town.php中给出的布尔值