Recursive cte with values from 2 tables - sql-server

Question

I need some help with this please.
I would like to create a recursive query with values from a table for the anchor, multiplied by a coefficient from another table.
Let me be more explicit :
Tables structure and filling :
create table T
(
Site varchar(10) primary key,
Price money,
Year int
);
create table B
( Site varchar(10),
Coeff float,
Year int
);
insert into T values /* Each Site appears only once here */
('A', 125.10, 2003),
('B', 78.10, 2002),
('C', 23.34, 2001)
insert into B values /* Each (Site,Year) appears only once here */
('A', 12, 2003),
('A', 0.111, 2004),
('B', 0.322, 2002),
('B', 0.333, 2003),
('C', 0.555, 2001),
('C', 0.666, 2002)
My recursive formula is :
Price (n) = Price (n-1)* Coeff(n-1)
(where n is the year)
Here is my last attempt :
;WITH cte
AS (SELECT T.Site, T.Year, T.Price as RootPrice FROM T
UNION ALL
SELECT T.Site, T.Year, CAST(cte.RootPrice * B.Coeff AS MONEY) AS PriceYear
FROM T INNER JOIN cte ON T.Site = cte.Site AND T.Year = cte.Year INNER JOIN B ON cte.Year = B.Year AND cte.Site = B.Site)
SELECT * FROM cte
This cte is running endlessly. What am I missing ?
Edit :
Output needed :
Site | Price | Year
---------------------------
A | 1501.2 | 2003
A | 166.78 | 2004
B | 25.15 | 2002
B | 8.37 | 2003
C | 12.95 | 2001
C | 8.63 | 2002

Answer 1

This produces the output you want:
;WITH CTE AS
(
SELECT
Site = T.Site,
Year = T.Year,
Price = CONVERT(MONEY, T.Price * B.Coeff)
FROM
T AS T
INNER JOIN B AS B ON
T.Site = B.Site AND
T.Year = B.Year
UNION ALL
SELECT
Site = C.Site,
Year = C.Year + 1,
Price = CONVERT(MONEY, C.Price * B.Coeff)
FROM
CTE AS C
INNER JOIN B AS B ON
C.Site = B.Site AND
C.Year + 1 = B.Year
)
SELECT
*
FROM
CTE AS C
ORDER BY
C.Site,
C.Year
The problem with your solution is that the anchor doesn't start with the correct price, you should multiply the price with coeff on the anchor. Keep in mind that the anchor is the first set of the resulting CTE and it is included in it.
So your anchor:
SELECT
T.Site,
T.Year,
T.Price as RootPrice
FROM
T
Should start with the correct price for that year:
SELECT
Site = T.Site,
Year = T.Year,
Price = CONVERT(MONEY, T.Price * B.Coeff)
FROM
T AS T
INNER JOIN B AS B ON
T.Site = B.Site AND
T.Year = B.Year
And remove the T reference on the recursive set, since you don't need it anymore.
If you also want to see the root prices, you can tamper a little with the recursive join expression:
;WITH CTE AS
(
SELECT
Site = T.Site,
Year = T.Year,
Price = T.Price,
IsRoot = 1
FROM
#T AS T
UNION ALL
SELECT
Site = C.Site,
Year = CASE WHEN C.IsRoot = 1 THEN C.Year ELSE C.Year + 1 END,
Price = CONVERT(MONEY, C.Price * B.Coeff),
IsRoot = 0
FROM
CTE AS C
INNER JOIN #B AS B ON C.Site = B.Site
WHERE
(C.IsRoot = 1 AND C.Year = B.Year) OR
(C.IsRoot = 0 AND C.Year + 1 = B.Year)
)
SELECT
*
FROM
CTE AS C
ORDER BY
C.Site,
C.Year,
C.IsRoot DESC
/*
Results:
Site Year Price IsRoot
---------- ----------- --------------------- -----------
A 2003 125,10 1
A 2003 1501,20 0
A 2004 166,6332 0
B 2002 78,10 1
B 2002 25,1482 0
B 2003 8,3744 0
C 2001 23,34 1
C 2001 12,9537 0
C 2002 8,6272 0
*/