MySQL无法识别我的HTML表单选择值

<form action="insert.php" method="POST">
  <label for="myselect">选择值：</label>
  <select name="myselect" id="myselect">
    <option value="value1">值1</option>
    <option value="value2">值2</option>
    <option value="value3">值3</option>
  </select>
  <input type="submit" value="提交">
</form>

<?php
// 连接到MySQL数据库
$servername = "数据库服务器地址";
$username = "数据库用户名";
$password = "数据库密码";
$dbname = "数据库名称";
$conn = new mysqli($servername, $username, $password, $dbname);

// 检查连接是否成功
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

// 获取表单选择值
$myselect = $_POST['myselect'];

// 将选择值插入到MySQL数据库中的表
$sql = "INSERT INTO 表名 (列名) VALUES ('$myselect')";

if ($conn->query($sql) === TRUE) {
    echo "数据插入成功";
} else {
    echo "数据插入失败: " . $conn->error;
}

// 关闭数据库连接
$conn->close();
?>