select restaurant_name,

sum_price,

sum_quantity,

case when sum_quantity<=5 then 0.1

when sum_quantity>15 and sum_prine>=300000 then 0.005

else 0.01 end discount_rate

from

(

select restaurant_name

sum(price) sum_prine

sum(quantity) sum_quantity

from food_orders

group by 1

)a