php - MySQL不插入NULL值

这对你来说很容易，但我是个笨蛋，所以我需要帮助。
这是我的代码，不管是什么原因，else语句没有执行。如果我更改$variable=NULL的空值，它会工作，但会在数据库中输入空字符串，而不是空值。有人能帮忙解释一下原因吗？

if (isset($_POST['agreeto']))
{
    $enter_feedback = "INSERT INTO feedback" . //(initial, surname, country_id, date, friend_score, return_score, service_score, comments)
        " VALUES('" . $initial. "', '" . $lastname . "', '" . $country_id . "', NOW(),  '" . $friend . "', '" . $return . "', '" . $service . "', '" . $_POST['comments'] . "')";
}else
{
    $enter_feedback = "INSERT INTO feedback" . //(initial, surname, country_id, date, friend_score, return_score, service_score, comments)
    " VALUES('" . $initial. "', '" . $lastname . "', '" . $country_id . "', NOW(),  '" . $friend . "', '" . $return . "', '" . $service . "', " . NULL . ")" or die("couldn't execute my query");
}

最佳答案

MySQL需要字符串=NULL，您将传递php NULL常量的值。

if (isset($_POST['agreeto']))
                {
                    $enter_feedback = "INSERT INTO feedback" . //(initial, surname, country_id, date, friend_score, return_score, service_score, comments)
                    " VALUES('" . $initial. "', '" . $lastname . "', '" . $country_id . "', NOW(),  '" . $friend . "', '" . $return . "', '" . $service . "', '" . $_POST['comments'] . "')";
                }else
                    {
                        $enter_feedback = "INSERT INTO feedback" . //(initial, surname, country_id, date, friend_score, return_score, service_score, comments)
                        " VALUES('" . $initial. "', '" . $lastname . "', '" . $country_id . "', NOW(),  '" . $friend . "', '" . $return . "', '" . $service . "',NULL)" or die("couldn't execute my query");
                    }

关于php - MySQL不插入NULL值，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/18873665/