ajax怎么连接MySQL数据库

<?php
$servername = "数据库主机名";
$username = "数据库用户名";
$password = "数据库密码";
$dbname = "数据库名称";

// 创建数据库连接
$conn = new mysqli($servername, $username, $password, $dbname);

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

// 执行SQL查询操作
$sql = "SELECT * FROM 表名";
$result = $conn->query($sql);

// 处理查询结果
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "字段1: " . $row["字段1"]. " - 字段2: " . $row["字段2"]. "<br>";
    }
} else {
    echo "没有结果";
}

// 关闭数据库连接
$conn->close();
?>