Table name from Subquery [SQL]

I was looking for the column "age" from table B, but when I used "b.age", it resulted in an error.

 

Error code

SELECT a.cuisine_type,
	   a.price,
	   할인률,
	   b,age, 
	 a.price-(price*할인률) 'after_discount'
FROM 
(
SELECT a.cuisine_type,
	   a.price,
	   b.age,
	   if(b.age>50,(b.age-50)*0.005,0) '할인률'
from food_orders a left join customers b on a.customer_id=b.customer_id
) a
order by 할인률 desc

 

 

 

The error occurred because the new query retrieves data from the subquery, so it couldn't find table B as all the data is sourced from subquery A.