php动态变量并排数组插入数据库问题

$servername = "数据库服务器";
$username = "用户名";
$password = "密码";
$dbname = "数据库名称";

$conn = new mysqli($servername, $username, $password, $dbname);

if ($conn->connect_error) {
    die("数据库连接失败: " . $conn->connect_error);
}

$student1_name = "张三";
$student1_age = 20;
$student1_grade = "大一";

$student2_name = "李四";
$student2_age = 21;
$student2_grade = "大二";

$students = array(
    array("name" => $student1_name, "age" => $student1_age, "grade" => $student1_grade),
    array("name" => $student2_name, "age" => $student2_age, "grade" => $student2_grade)
);

$stmt = $conn->prepare("INSERT INTO students (name, age, grade) VALUES (?, ?, ?)");

foreach ($students as $student) {
    $stmt->bind_param("sis", $student["name"], $student["age"], $student["grade"]);
    $stmt->execute();
}

$stmt->close();

$conn->close();