payee and payer are in the same column. What can I do to search within both.

$g->select_command = "SELECT id,code,date,payer,payee,amount_dvz,status,amount,kurkodu,accdes,type,accname from sys_transactions WHERE firmaid=$firmaid AND category='Havale'";

$col = array();
        $col["title"] = "Hesap Kartı";
        $col["name"] = "payee";
        $col["width"] = '100';
        $col["search"] = true;
        $col["on_data_display"] = array("display_stage_banka", "");
        function display_stage_banka($data)
        {

            $op = $data["payer"];
            $op2 = $data["payee"];

            if ($op!=''){
                return $op;
            }else{
                return $op2;

            }

        }

        $cols[] = $col;