SELECT * FROM `orders` WHERE `user_id`='" . $_SESSION["user"]["id"] . "' and 'status' = 'Активен'select sum(row_size)
from (
select
char_length(column1)+
char_length(column2)+
char_length(column3)+
char_length(column4) ... <-- перечисляем здесь все колонки
as row_size
from your_table
) as tbl1;