t1 =（从请求的
中选择quantity_app
，其中requested_id =

_POST [hidden]）;

t2 =更新仓库
设定数量=数量 - 。

my query is here:

$t1 = "(select quantity_app
        from requested
        where requested_id = $_POST[hidden])";
$t2 = "update warehouse
       set quantity = quantity - " . $t1;

this query doesn't run please help me i don't know were i do it wrong!
the quantity_app column must subtract quantity column

t1 = "(select quantity_app from requested where requested_id =

_POST[hidden])";

t2 = "update warehouse set quantity = quantity - " .