Average price change over a period of time SQL - sql

Question

Trying to get the average price change for several items. This is my first time using SQL server, coming from some light experience in Oracle SQL and MySQL. The table is set up like this:
ProductID
StartDate
EndDate
StandardCost
707
5/31/11
5/29/12
12.2
707
5/30/12
5/29/13
13
707
5/30/13
null
13.5
708
5/31/11
5/29/12
10
708
5/30/12
5/29/13
11
708
5/30/13
null
12
I would like it to return this:
ProductID
Difference
707
1.3
708
2
with a as
(
select
productID, standardcost, startDate, ISNULL(endDate, GETDATE())
from
production.ProductCostHistory
where (productID, endDate) in (select
productID, max(endDate)
from
Production.ProductCostHistory
group by
productID
)
),
b as
(
select
productID, standardcost, startDate, startDate
from
production.ProductCostHistory
where (productID, startDate) in (select
productID, min(StartDate)
from
Production.ProductCostHistory
group by
productID
)
)
select
a.productID, (a.standardcost - b.standardcost) difference
from
a join b
on a.ProductID = b.ProductID and
a.startDate = b.startDate and
a.EndDate = b.EndDate
The idea is to first get the price with the most recent end date, then subtract the price from the oldest start date, to get the change in cost over that period of time. I understand that the where ... in does not work like in Oracle SQL, but I have not found a way to use exists the way that I need it to work. The averaging will be done in PowerBI, so I'm not worried about doing that in the Query. I would appreciate any help. Thanks.

Answer 1

You can try calculating the Standardcosts corresponding to the first startdate, and latest enddate (for each product) using an analytic function FIRST_VALUE.
select
productid,
max(fv) as value_at_first_startdate,
max(lv) as value_at_latest_enddate,
diff = max(lv) - max(fv)
from (
select
productid,
first_value(standardcost)
over (partition by productid
order by startdate) as fv,
first_value(standardcost)
over (partition by productid
order by case when enddate is null then 0 else 1 end
, enddate desc) as lv
from cte
) t
group by productid

Answer 2

Assuming your SQL is supposed to return correct result:
with minmax (productId, minStart, maxEnd) as
( select
productID, min(startDate),max(endDate)
from
Production.ProductCostHistory
group by productID
),
a as
(
select
p.productID, standardcost, startDate, ISNULL(endDate, GETDATE())
from production.ProductCostHistory p
inner join minmax m on m.productId = p.productId AND
m.maxEnd = p.endDate
),
b as
(
select
p.productID, standardcost, startdate, startdate
from production.ProductCostHistory p
inner join minmax m on m.productId = p.productId AND
m.minStart = p.startDate
)
select
a.productID, (a.standardcost - b.standardcost) difference
from
a join b
on a.ProductID = b.ProductID and
a.startDate = b.startDate and
a.EndDate = b.EndDate