PHPでデータベースからデータを取得した際の返り値

$pdo = new PDO($dsn, $user, $pwd);
$pdo->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);
$pst = $pdo->query('select * from table_name');
// $result = $pst->fetchALL(PDO::FETCH_ASSOC);
$result = $pst->fetchALL();

echo ('<pre>');
print_r($result);
echo ('</pre>');

Array
(
    [0] => Array
        (
            [column_name] => value
        )
)

$pdo = new PDO($dsn, $user, $pwd);
$pdo->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);
$pst = $pdo->query('select * from table_name');
$result = $pst->fetch();

echo ('<pre>');
print_r($result);
echo ('</pre>');

Array
(
    [column_name] => value
)