如何用php和mysql做一个组合框？

<?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";

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

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

// 查询选项数据
$sql = "SELECT value, label FROM options";
$result = $conn->query($sql);

// 构建HTML组合框
echo "<select>";
if ($result->num_rows > 0) {
    while ($row = $result->fetch_assoc()) {
        echo "<option value='" . $row["value"] . "'>" . $row["label"] . "</option>";
    }
}
echo "</select>";

// 关闭数据库连接
$conn->close();
?>