combining two different record into single result
You should use GROUP_CONCAT on emp_first_name. Maybe something like:

$this-&gt;datatables
   -&gt;select('o.order_id, 
        concat_ws(" " , `l.location_street`, `l.location_city` ) as location_address, 
        group_concat(e.emp_first_name SEPARATOR ','), o.order_status, o.from_date')
   -&gt;from('orders o')
   -&gt;join('location l', 'o.location_id = l.location_id')
   -&gt;join('order_details od', 'od.order_id = o.order_id')
   -&gt;join('employee e', 'e.emp_id = od.emp_id')
   -&gt;group_by('o.order_id');