1.普通连接

$mysql_server = 'localhost';
$mysql_username = '用户名';
$mysql_password = '用户密码';
$mysql_database = '数据库名';//建立数据库连接
$conn = mysql_connect($mysql_server, $mysql_username, $mysql_password) or die('数据库连接失败！');
//选择某个数据库
mysql_select_db($database, $conn);
//编码转化
mysql_query("set names 'utf8'");
//执行sql
$result = mysql_query(select * from database where id=1);
//提取数据
$row=mysql_fetch_row($result);

在提取数据的时候，我们使用mysql_fetch_row，还可以使用mysql_fetch_assoc和mysql_fetch_array

2.面向对象方法mysqli连接

$mysql_conf = array(
    'host'      => '127.0.0.1:3306', 
    'username'  => 'root', 
    'password'  => '123456', 
    'database'  => 'test', 
);
$db = new mysqli($mysql_conf['host'], $mysql_conf['username'], $mysql_conf['password'], $mysql_conf['database']);
if(mysqli_connect_error()){  
    die("could not connect to the database:\n" . $mysqli->connect_error);//诊断连接错误
}
$result = $db->query("select * from database where id=1");
$row = $result->fetch_array();

3、PDO方法连接

try {
    //配置信息
    $dsn = 'mysql:dbname=test;host=localhost';
    $username = 'root';
    $password = '123456';
    $attr = [
        PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION
    ];
    //创建一个pdo对象
    $pdo = new PDO($dsn, $username, $password, $attr);
    //编码转化
    $pdo->exec("set names 'utf8'");
    //编写sql
    $sql = "select * from user where name = :name";
    //预处理
    $stmt = $pdo->prepare($sql);
    $data = [
        ':name' => 'john'
    ];
    //执行
    $stmt->execute($data);
    // PDO::FETCH_ASSOC 关联数组形式
    // PDO::FETCH_NUM   数字索引数组形式
    $res = $stmt->fetchAll(PDO::FETCH_ASSOC);
    if ($res) {
        die('查询成功');
    } else {
        die('查询失败');
    }
    $pdo = null;//关闭连接
} catch(PDOException $e) {
    //异常
    echo $e->getMessage();
}