Unpivotting multiple columns - substring of column name as a new column with CROSS APPLY - sql-server

Question

I have a table with the following format
YEAR, MONTH, ITEM, REQ_QTY1, REQ_QTY2 , ....REQ_QTY31 ,CONVERTED1, CONVERTED2 ....CONVERTED31
Where the suffix of each column is the day of the month.
I need to convert it to the following format, where Day_of_month is the numeric suffix of each column
YEAR, MONTH, DAY_OF_MONTH, ITEM, REQ_QTY, CONVERTED
I thought of using CROSS APPLY to retrieve the data, but I can't use CROSS APPLY to get the "Day of Month"
SELECT A.YEAR, A.MONTH, A.ITEM, B.REQ_QTY, B.CONVERTED
FROM TEST A
CROSS APPLY
(VALUES
(REQ_QTY1, CONVERTED1),
(REQ_QTY2, CONVERTED2),
(REQ_QTY3, CONVERTED3),
......
(REQ_QTY31, CONVERTED31)
)B (REQ_QTY, CONVERTED)
The only way I found is to use a nested select with inner join
SELECT A.YEAR, A.MONTH, A.DAY_OF_MONTH, A.ITEM,A.REQ_QTY, D.CONVERTED FROM
(SELECT YEAR, MONTH, ITEM, SUBSTRING(DAY_OF_MONTH,8,2) AS DAY_OF_MONTH, REQ_QTY FROM TEST
UNPIVOT
(REQ_QTY FOR DAY_OF_MONTH IN ([REQ_QTY1],[REQ_QTY2],[REQ_QTY3],......[REQ_QTY30],[REQ_QTY31])
) B
) A
INNER JOIN (SELECT YEAR, MONTH, ITEM, SUBSTRING(DAY_OF_MONTH,10,2) AS DAY_OF_MONTH, CONVERTED FROM TEST
UNPIVOT
(CONVERTED FOR DAY_OF_MONTH IN ([CONVERTED1],[CONVERTED2],[CONVERTED3],....[CONVERTED30],[CONVERTED31])
) C
) D
ON D.YEAR = A.YEAR AND D.MONTH = A.MONTH AND D.ITEM = A.ITEM AND D.DAY_OF_MONTH = A.DAY_OF_MONTH
Is there a way to use CROSS APPLY and yet get the DAY_OF_MONTH out?

Answer 1

This is not a solution with CROSS APPLY but it will definitely make it a bit faster as it uses a bit simpler approach and simpler execution plan.
SQL Fiddle
MS SQL Server 2008 Schema Setup:
CREATE TABLE Test_Table([YEAR] INT, [MONTH] INT, [ITEM] INT, REQ_QTY1 INT
, REQ_QTY2 INT ,REQ_QTY3 INT , CONVERTED1 INT, CONVERTED2 INT, CONVERTED3 INT)
INSERT INTO Test_Table VALUES
( 2015 , 1 , 1 , 10 , 20 , 30 , 100 , 200 , 300),
( 2015 , 2 , 1 , 10 , 20 , 30 , 100 , 200 , 300),
( 2015 , 3 , 1 , 10 , 20 , 30 , 100 , 200 , 300)
Query 1:
SELECT *
FROM
(
SELECT [YEAR]
,[MONTH]
,ITEM
,Vals
,CASE WHEN LEFT(N,3) = 'REQ' THEN SUBSTRING(N,8 ,2)
WHEN LEFT(N,3) = 'CON' THEN SUBSTRING(N,10,2)
END AS Day_Of_Month
,CASE WHEN LEFT(N,3) = 'REQ' THEN LEFT(N,7)
WHEN LEFT(N,3) = 'CON' THEN LEFT(N,9)
END AS Tran_Type
FROM Test_Table t
UNPIVOT (Vals FOR N IN ([REQ_QTY1],[REQ_QTY2],[REQ_QTY3],
[CONVERTED1],[CONVERTED2],[CONVERTED3]))up
)t2
PIVOT (SUM(Vals)
FOR Tran_Type
IN (REQ_QTY, CONVERTED))p
Results:
| YEAR | MONTH | ITEM | Day_Of_Month | REQ_QTY | CONVERTED |
|------|-------|------|--------------|---------|-----------|
| 2015 | 1 | 1 | 1 | 10 | 100 |
| 2015 | 1 | 1 | 2 | 20 | 200 |
| 2015 | 1 | 1 | 3 | 30 | 300 |
| 2015 | 2 | 1 | 1 | 10 | 100 |
| 2015 | 2 | 1 | 2 | 20 | 200 |
| 2015 | 2 | 1 | 3 | 30 | 300 |
| 2015 | 3 | 1 | 1 | 10 | 100 |
| 2015 | 3 | 1 | 2 | 20 | 200 |
| 2015 | 3 | 1 | 3 | 30 | 300 |

Answer 2

Well, I found a way using CROSS APPLY, but instead of taking a substring, I'm basically hardcoding the days. Works well enough so...
SELECT A.YEAR, A.MONTH, A.ITEM, B.DAY_OF_MONTH, B.REQ_QTY, B.CONVERTED
FROM TEST A
CROSS APPLY
(
VALUES
('01', REQ_QTY1, CONVERTED1),
('02', REQ_QTY2, CONVERTED2),
('03', REQ_QTY3, CONVERTED3),
('04', REQ_QTY4, CONVERTED4),
......
('31', REQ_QTY31, CONVERTED31)
) B (DAY_OF_MONTH, REQ_QTY, CONVERTED)