How to send php query data to the front end

PHP is a commonly used back-end language in web development. Sometimes it is necessary to query data from the database and transfer it to the front-end page so that users can view and use the data. In this article, we will introduce how to query the database in PHP and transfer the data to the front end so that you can develop more complex web applications.

1. Connect to the database

Before using PHP to query the database, you need to establish a connection with the database first. Connecting to the database using PHP can be achieved through PHP's mysqli and PDO extensions. The specific steps are as follows:

1. Use mysqli extension to connect to the database:

$servername = "localhost"; // 数据库主机名
$username = "username"; // 数据库用户名
$password = "password"; // 数据库密码
$dbname = "myDB"; // 数据库名

// 创建连接
$conn = mysqli_connect($servername, $username, $password, $dbname);

// 检查连接是否成功
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

2. Use PDO extension to connect to the database:

$servername = "localhost"; // 数据库主机名
$username = "username"; // 数据库用户名
$password = "password"; // 数据库密码
$dbname = "myDB"; // 数据库名

// 创建连接
try {
    $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
    // 设置 PDO 错误模式为异常
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    echo "Connected successfully";
} catch(PDOException $e) {
    echo "Connection failed: " . $e->getMessage();
}

2. Query data

After successfully connecting to the database, you can query the data. Querying the database using PHP can be achieved through mysqli and PDO extensions. The specific steps are as follows:

1. Use mysqli to expand query data:

$sql = "SELECT id, name, email FROM users";
$result = mysqli_query($conn, $sql);

if (mysqli_num_rows($result) > 0) {
    // 输出数据
    while($row = mysqli_fetch_assoc($result)) {
        echo "id: " . $row["id"]. " - Name: " . $row["name"]. " - Email: " . $row["email"]. "<br>";
    }
} else {
    echo "0 results";
}

2. Use PDO to expand query data:

$sql = "SELECT id, name, email FROM users";
$result = $conn->query($sql);

if ($result->rowCount() > 0) {
    // 输出数据
    while($row = $result->fetch()) {
        echo "id: " . $row["id"]. " - Name: " . $row["name"]. " - Email: " . $row["email"]. "<br>";
    }
} else {
    echo "0 results";
}

The above code The values ​​of the id, name and email fields will be queried from the database table named "users". If the data is queried, the data will be output to the front end. If no data is found, "0 results" is output.

3. Send data to the front-end

After querying the data, you need to send them to the front-end page. In PHP, data can be passed to the frontend via JSON format. The specific steps are as follows:

1. Encode data into JSON format:

$sql = "SELECT id, name, email FROM users";
$result = mysqli_query($conn, $sql);

$data = array();
if(mysqli_num_rows($result) > 0) {
    while($row = mysqli_fetch_assoc($result)) {
        $data[] = $row;
    }
}

$json = json_encode($data);

2. Transmit JSON data to the front end:

Use AJAX technology can asynchronously transmit server-side data to the front-end, allowing the front-end page to display data more quickly.

<script>
    var xmlhttp = new XMLHttpRequest();
    var url = "getdata.php";

    xmlhttp.onreadystatechange = function() {
        if (this.readyState == 4 && this.status == 200) {
            var data = JSON.parse(this.responseText);
            // 将数据渲染至前端页面
            // ...
        }
    };

    xmlhttp.open("GET", url, true);
    xmlhttp.send();
</script>

The above code will obtain data in JSON format from the file named "getdata.php" and render the data to the front-end page.

Conclusion

Through the introduction of this article, you have learned how to connect to the database, query data and transfer data to the front-end page in PHP. At the same time, we also introduced common ways to use JSON to transfer data. Now, you can use these techniques to develop more complex web applications.

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