PHP在下拉列表中显示从数据库输入空值的空值

<?php
// 连接数据库
$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";
$conn = new mysqli($servername, $username, $password, $dbname);

// 查询数据
$sql = "SELECT id, name FROM your_table";
$result = $conn->query($sql);

// 构建下拉列表
echo "<select>";
echo "<option value=''>-请选择-</option>"; // 显示空值选项
if ($result->num_rows > 0) {
    while ($row = $result->fetch_assoc()) {
        $id = $row["id"];
        $name = $row["name"];
        echo "<option value='$id'>$name</option>";
    }
}
echo "</select>";

// 关闭数据库连接
$conn->close();
?>