之间有什么区别：“not variable is null”和“variable is not null”？

Question

我是SQL的新手，我想知道是否有任何区别：

     // Adding customer 
// pass cust_name,phone,address and apikey
    $app->post('/customer', function ($request, $response, $args) {
                    $_message = $request->getParsedBody();
                    $customer = new Customer();
                    $customer->cust_name = $_message['cust_name'];
                    $customer->phone     = $_message['phone'];
                    $customer->address   = $_message['address'];
                    $customer->apikey    = $_message['apikey'];
                    $payload=[];
                    $customer->save();
                    if ($customer->id) {
                        $payload = ['cust_id'   => $customer->id,
                                    'cust_uri' => '/customer/' . $customer->id
                                    ];
                 return $response->withStatus(201)->withJson($payload);
                    }else {
                        return $response->withStatus(400);
                    }


            });

和

not variable is null

Answer 1

实际上两个术语都没有区别。它们都指的是变量的可空性。

如果有任何差异，那么阅读的简单性。