Interview question:How to get last 3 month aggregation at column level?

Question

This is the question i was being asked at Apple onsite interview and it blew my mind. Data is like this:

orderdate,unit_of_phone_sale

20190806,3000

2019070         


        

Answer 1

You can use this query:

select a.order_month, a.unit_of_phone_sale, 
LEAD(unit_of_phone_sale, 1, 0) OVER (ORDER BY rownum) AS M_1,
LEAD(unit_of_phone_sale, 2, 0) OVER (ORDER BY rownum) AS M_2,
LEAD(unit_of_phone_sale, 3, 0) OVER (ORDER BY rownum) AS M_3
from (
select TO_CHAR(orderdate, 'YYYYMM') order_month,
unit_of_phone_sale,
rownum
from Y
order by order_month desc) a