随机查询失败MySql

Question

我希望这个问题不是太宽泛，但不是特定的代码。基本上在随机时间和随机查询中我的代码都出现故障。大多数情况下，它似乎是我的INSERT调用。更新和删除仍然可以正常工作，但INSERT将在整个页面上失败几个小时，然后再次神秘地工作。该页面目前仅由我自己使用和测试。

其中一个示例查询。 PHP

session_start();
    $poster = $_SESSION['login_user'];
    $conn = new PDO("mysql:host=localhost;dbname=spectrum",'root', '1234abcd');
    $u = $_POST['user'];
    $p = md5($_POST['pass']);
    $e = $_POST['email'];
    $fn = $_POST['first_name'];
    $ln = $_POST['last_name'];
    $t = $_POST['type'];
    $sql = "INSERT INTO users(id, user, pass, email, type, first_name, last_name, poster) VALUES ('', :user, :pass, :email, :type, :first, :last, :poster)";
    $q = $conn->prepare($sql);
    $q->bindParam(":user", $u);
    $q->bindParam(":email", $e);
    $q->bindParam(":pass", $p);
    $q->bindParam(":type", $t);
    $q->bindParam(":first", $fn);
    $q->bindParam(":last", $ln);
    $q->bindParam(":poster", $poster);
    $q->execute();
    echo json_encode('User has been added.');

这是通过Ajax调用完成的。 JQuery的

var request;
        if (request) {
                request.abort();
            }
            var $form = f;
            var $inputs = $form.find("input, select, button, textarea");
            var serializedData = $form.serialize();
            $inputs.prop("disabled", true);
            request = $.ajax({
                url: site + "/backend/formup.inc.php",
                type: "post",
                dataType: 'json',
                data: serializedData
            });
            request.done(function (data){
                    if(data.location){
                        window.location.replace(data.location);
                    }
                    else{
                        alert(data);
                        location.reload(false);
                    }

            });
            request.fail(function (jqXHR, textStatus, errorThrown){
                alert(
                    "The following error occured: "+
                    textStatus, errorThrown
                );
            });

            request.always(function (data) {
                if(!data.tvar){
                    $inputs.prop("disabled", false);
                }
            });

这是HTML。

<form class="hidden" method="POST">
                    <input type="text" name="user" placeholder="Username" required/>
                    <input type="email" name="email" placeholder="Email" required/>
                    <input type="password" name="pass" placeholder="Password" required/>
                    <input type="text" name="first_name" placeholder="First Name" required/>
                    <input type="text" name="last_name" placeholder="Last Name" required/>
                    <input type="radio" name="type" value="0">Owner
                    <input type="radio" name="type" value="1">Employee
                    <input type="radio" name="type" value="2">Artist
                    <input type="radio" name="type" value="3">Venue
                    <input type="radio" name="type" value="4">Fan<br />
                    <input type="hidden" name="fname" value="add_user" />
                    <input type="submit" class="button" value="Add" />
                </form>

如果我的问题可能会出现某些格式错误，我也很抱歉。第一次发布并习惯了网站。