PHP의 다양한 데이터베이스 관리 시스템 간의 연결 차이점

<?php
$servername = "localhost";
$username = "username";
$password = "password";

// 创建一个 MySQL 连接
$conn = new mysqli($servername, $username, $password);

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

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "database_name";

// 创建一个 PostgreSQL 连接
$conn = new PDO("pgsql:host=$servername;port=5432;dbname=$dbname", $username, $password);

// 检查连接
if (!$conn) {
    die("连接失败：" . pg_last_error());
}
?>

<?php
$servername = "localhost";
$port = 27017;
$dbname = "database_name";

// 创建一个 MongoDB 连接
$client = new MongoDB\Client("mongodb://localhost:27017");

// 选择数据库
$db = $client->selectDatabase($dbname);
?>

<?php
// 创建一个 MySQL 连接
$conn = new mysqli($servername, $username, $password);

// 准备一个 SQL 查询
$sql = "SELECT * FROM employees";

// 执行查询
$result = $conn->query($sql);

// 如果查询成功，则遍历结果
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "员工姓名： " . $row["first_name"] . " " . $row["last_name"] . "<br>";
    }
} else {
    echo "没有记录找到";
}
?>