我在我的主页上通过ajax异步运行了以下.php文件，该主页本应提交评论：

<?php
session_start();
include "dxbase.php";
$conn = new mysqli($servername, $username, $password, $dbname);

    $comment = "practice";
    $prid = 2;

    if(isset($_SESSION['user'])){

    $usera = $_SESSION['user'];

    $stmt = $conn->prepare("INSERT INTO reviews (prid, content, username) VALUES (?, ?, ?)");
    $stmt->bind_param("sss", $prid, $comment, $usera);
    $stmt->execute();
    echo "Review submitted!";
    $stmt->close();

    } else {
        echo "Oops! You need to be signed in to review products!";

    }
    $conn->close();
?>

当我运行它时，它回显它已经提交了一条评论，但当我检查我的数据库时，它不在那里：db
为什么不插？！