MYSQL计算group_concat项的总和

Question

i have a group_concat in my query and due to this i cannot have the actual some of the concated values because of the separation is limited between the values, so i need to get the total sum of the concated values instead of the values it self...

my query

. "GROUP_CONCAT(if (sma_sale_items.item_tax >0,round(sma_sale_items.net_unit_price * " . $this->db->dbprefix('sale_items') . ".quantity,2),'
') SEPARATOR '
') as unitp,"

which will result in :

1
1
1
1
1

what i need is:

5

any ideas please ?!??!

PS: am using phpexcel to echo the values so if there is an idea from there it would also be great

$this->excel->getActiveSheet()->SetCellValue('F' . $row, $data_row->unitp);