使用PHP在DATETIME字段中添加9个小时

i am getting DATETIME field from server.

$result = $mysqli->query("SELECT * FROM table");

while($row = $result->fetch_array()){

     echo $row['add_time']; //2016-02-15 21:45:52
}

I want to add 9 hours to $row['add_time'] so i can get 2016-02-16 06:45:52. How can i do that using easiest way. i dont want to change datetime to seconds while using strtotime().

NOTE: No, There is no similar question to that.

What about using DateTime/DateInterval?

echo new \DateTime($row['add_time'])->add(new DateInterval('P9H'))->format('Y-m-d H:i:s') ?

$row['add_time'] = date("Y-m-d H:i:s",strtotime($row['add_time']) + (3600 * 9));

Do it in the SQL:

$result = $mysqli->query("SELECT add_time + INTERVAL 9 HOUR FROM table");

while($row = $result->fetch_array()){

     echo $row['add_time']; //2016-02-15 21:45:52
}

You will get 2016-02-16 06:45:52