如何在Android中获取长文本类型数据？

I need to fetch long text type data from mysql server for Android application. It is showing NULL after encoding in JSON. Code is given below.

<?php
require_once('dbConnect.php');
$sql = "select tips from health_tips order by number";
$res = mysqli_query($con, $sql);
$result = array();
while ($row = mysqli_fetch_array($res))
{
    array_push($result, array('url' => $row['tips']));
}
echo json_encode(array("result" => $result));
mysqli_close($con);

How to solve this problem?

Any help will be appreciated.
Thanks.

first try debugging ..so that u can get the idea whether they are fetching any value or showing null..do debugging ur app.or else do on those line where u think need any change