如何使用PHP搜索多标准的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";

// 使用MySQLi连接数据库
$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
    die("连接数据库失败: " . $conn->connect_error);
}

// 使用PDO连接数据库
try {
    $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch(PDOException $e) {
    die("连接数据库失败: " . $e->getMessage());
}

$name = "John";
$age = 18;

$sql = "SELECT * FROM users WHERE name = '$name' AND age >= $age";

$result = $conn->query($sql);

if ($result->num_rows > 0) {
    while ($row = $result->fetch_assoc()) {
        // 处理每一行的数据
    }
} else {
    echo "没有找到匹配的结果";
}

$stmt = $conn->prepare($sql);
$stmt->execute();

if ($stmt->rowCount() > 0) {
    while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
        // 处理每一行的数据
    }
} else {
    echo "没有找到匹配的结果";
}