Problem order number with sql query

[sunaryaap]

Hello admin or all, can you help me.

I make a query for datatables in CI with Ignited-Datatables version 0.7, like this:
$this->datatables
->select(' @i := @i + 1 AS i,
concat(firstname, " ", lastname) AS fullname')
->join('(SELECT @i := 0) dummy', ' 1')
->from('db_member');

I aim for make a order number, like this : http://prntscr.com/67vn90
But I have a problem, sought after in the form results into a mess, like this : http://prntscr.com/67vnej

Do you have a solution ?

Thanks before :)