MYSQL Trigger Update column with same column based on other column -

i have following table.

order_id          code             value    1            sub_total          5.00    1            shipping           5.00    1            total              10.00    2            sub_total          3.00    2            shipping           6.00    2            total              9.00 

on occasion sub_total need update (products added instance), , total needs updated. have created trigger update sub_total. how update total based on sub_total , shipping?

i have attempted following:

create trigger after_order_product_update after update on order_product each row begin     update `order_total`      set `value` = new.`total` `order_id` = new.`order_id` , `code` = 'sub_total';      update `order_total`      set `value` = (select `value` `order_total` `code` = 'shipping' , `order_id` = new.`order_id`) + (select `value` `order_total` `code` = 'sub_total' , `order_id` = new.`order_id`) `code` = 'total' , `order_id` = new.`order_id`; end; 

here receive "you can't specify target table 'oc_order_total' update in clause error no: 1093"

create trigger after_order_product_update after update on order_product each row begin     declare sbvalue varchar(32);     declare shipvalue varchar(32);      update `order_total` set `value` = new.`total` `order_id` = new.`order_id` , `code` = 'sub_total';        set sbvalue = (select `value` `order_total` `code` = 'sub_total' , `order_id` = new.`order_id`);     set shipvalue = (select `value` `order_total` `code` = 'shipping' , `order_id` = new.`order_id`);      update `oc_order_total` set `value` = `sbvalue` + `shipvalue` `code` = 'total' , `order_id` = new.`order_id`; end; 

here receive "subquery returns more 1 row" error.

set sbvalue = (select `value` `order_total` `code` = 'sub_total'                 , `order_id` = new.`order_id` limit 1); set shipvalue = (select `value` `order_total` `code` = 'shipping'                , `order_id` = new.`order_id` limit 1); 

give limit 1 second query error..

hope helps