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select 
#ROUND((COUNT(CASE WHEN t2.order_date = t2.customer_pref_delivery_date THEN 1 END) / COUNT(*)) * 100, 2) AS #immediate_percentage
round((count(case when t2.order_date = t2.customer_pref_delivery_date  then 1 end)/count(*))*100 ,2)
as immediate_percentage 
from 
(select customer_id, min(order_date) as order_datefrom Deliverygroup by customer_id ) as t1
left join Delivery as t2 on t1.order_date = t2.order_date and t1.customer_id  = t2.customer_id