2.5 percent increase of previous field? - sql

Question

I have a table with a series of IDs. Each ID has dates ranging up to year 2025 from current year. Each year for each ID has a specific price.
http://i.imgur.com/srplSDo.jpg
Once I get to a certain point with each ID, it no longer has a specific price. So what I am wanting to do is take the previous years price and increase it by 2.5 percent. I have figured a way to grab the previous years price with this
SELECT a.*,
(CASE
WHEN a.YEARLY_PRICING is not null
THEN a.YEARLY_PRICING
ELSE (SELECT b.YEARLY_PRICING
FROM #STEP3 b
WHERE (a.id = b.id) AND (b.YEAR = a.YEAR-1))*1.025
END) AS TEST
FROM #STEP3 a
which would provide these results:
http://imgur.com/MJutM99
but the problem I am having is after the first null year, it is still recognizing the previous yearly_pricing as null, which gives me the null results, so obviously this method won't work for me. Any other suggestions for improvement?
Thanks

Answer 1

WITH CTE AS
(
SELECT ID, Year, Price, Price AS Prev
FROM T A
WHERE Year = (SELECT min(year) FROM T WHERE T.ID = A.ID GROUP BY T.ID)
UNION ALL
SELECT T.ID, T.Year, T.Price, ISNULL(T.Price, 1.025*Prev)
FROM T JOIN CTE ON T.ID = CTE.ID
AND T.Year - 1 = CTE.YEAR
)
SELECT * FROM CTE
ORDER BY ID, Year
SQL Fiddle Demo

Answer 2

What you want is a way to find not just the previous year (year - 1), but instead the year that is previous and also has a not-null price. To query for such a year (without solving your problem), you would do something like this:
select a.*
, (select max(year)
from step3 b
where a.id=b.id and a.year>b.year and b.yearly_pricing is not null
) PRIOR_YEAR
from step3 a
Since SQL-Server allows common-table expressions, you can call the above query "TMP", and then approach it this way. The CALC_PRICE in any year will be the price from the "PRIOR_YEAR" found as per the above query, multiplied by factor. That factor will be 1.025 to the POWER of the number of years from "PRIOR_YEAR" to the current year.
You would end up with SQL like this:
with TMP AS (
select a.*
, (select max(year)
from step3 b
where a.id=b.id and a.year>b.year and b.yearly_pricing is not null
) PRIOR_YEAR
from step3 a
)
select t.*,
c.yearly_pricing As prior_price,
c.yearly_pricing * POWER(1.025 , (t.year-t.prior_year)) calc_price
from tmp t
left join step3 c
on t.id=c.id and t.prior_year = c.year
It still has nulls, etc. but those are easily handled with COALESCE() or CASE expressions like you had in your question.
Here's an SQL Fiddle which shows how it works: http://sqlfiddle.com/#!3/296a4/21