php - Pull data from MySQL into JSONArray (with PDO!) -

i reading on internet , many people it's recommended switch pdo old mysql (and mysqli) extensions.

i'm new pdo, learned it. problem tried search stackoverflow, google, etc, didn't helped me.

original script mysqli :

$data = mysqli_query($con, "select x1, x2, x3, x4 table1 x1 = $variable1"); $row = mysqli_fetch_row($data); $result_data = array(   'data1' => $row[0],   'data2' => $row[1]  );  echo json_encode($result_data); 

this code outputs :

{"data1", 1, "data2", 2} 

i tried change pdo code :

 $sth = $dbh->prepare("select x1, x2, x3, x4 table1 x1 = ?");  $sth->bindparam(1, $variable1);  $sth->execute();  $row = $sth->fetchall();   $result_data = array(      'data1' => $row[0],     'data2' => $row[1],  );     echo json_encode($result_data); 

this me strange

{"data1", 1, 2, 1, "data2", 1, "data2"}, data1 null, data2 null 

it should original mysqli script...

i tried multiple fetch modes assoc, num, column, found on internet, result similar , error :

notice:undefined offset: 1 in

what can problem, how fix it?

 $sth = $dbh->prepare("select x1 data1, x2 data2 table1 x1 = ?");  $sth->execute([$variable1]);  echo json_encode($sth->fetchall(pdo::fetch_assoc));