如何在PHP和MySQL中使用PDO显示列值？

My code:

    $db1 = new PDO ( 'mysql:host=localhost;dbname=db;charset=utf8', 'root', '');
    $db1->setAttribute ( PDO::ATTR_ORACLE_NULLS, PDO::NULL_TO_STRING )
    $qry = $db1->prepare('SELECT user_name FROM user_data WHERE user_id = $userid LIMIT 1');
    $qry -> execute(array($userid));
    $row = $qry -> fetch();
    echo $qry -> user_name;

And it not eching nothing

And I want to find by $userid, and echo the user_name column(like user_id = 1 and it echo Name)

$db1 = new PDO ( 'mysql:host=localhost;dbname=db;charset=utf8', 'root', '');
$db1->setAttribute ( PDO::ATTR_ORACLE_NULLS, PDO::NULL_TO_STRING );
$qry = $db1->prepare("SELECT user_name FROM user_data WHERE user_id = ? LIMIT 1");
$qry -> execute(array($userid));
$row = $qry->fetch();
echo $row->user_name;

Change:

$qry = $db1->prepare('SELECT user_name FROM user_data WHERE user_id = $userid LIMIT 1');

For:

$qry = $db1->prepare('SELECT user_name FROM user_data WHERE user_id = ? LIMIT 1');

You will assign the value to user_id through execute statement

EDIT:

Add semicolon:

$db1->setAttribute ( PDO::ATTR_ORACLE_NULLS, PDO::NULL_TO_STRING ); <<<-- Missed semicolon