php - Having Issue on Getting json_encode() On Mysqli Prepared Statement -

i having problem on exporting result of prepared statement using mysqli.

$age = "young"; $rows = array(); $mysqli = new mysqli($db_hostname, $db_username, $db_password, $db_database);          $stmt = $mysqli->prepare("select fname, lname users age=?");         $stmt->bind_param('s', $age);         $stmt->execute();         $stmt->bind_result($thefname,$thelname);                 while($stmt->fetch())                    {                     array_push($rows, $thefname,$thelname);                   }             $stmt->close();  $mysqli->close(); echo json_encode($rows); 

as can see trying echo out json_encode($rows); each of rows json array :

[     {"firstname":"john", "lastname":"doe"},      {"firstname":"anna", "lastname":"smith"},      {"firstname":"peter","lastname":"jones"} ] 

but getting is

["john", "doe", "anna", "smith", "peter", "jones"]  

can please let me know why happening , how can fix it

push proper array -

array_push($rows, array('firstname' => $thefname, 'lastname' => $thelname));