Question

I know this may sounds silly but I would like to create function that will process data from tables with different size.

Lets say I have first table like so:

ID    IRR     M0    M1
----------------------
 1      0    -10     5
 2      0    -20    10
 3      0   -100   100
 4      0    -10     0

And second table like so:

ID    IRR     M0    M1    M2
----------------------------
 1      0    -10     5    60
 2      0    -20    10     0
 3      0   -100   100   400
 4      0    -10     0    10

I would like to create function that will be able to process data from both tables.

I know that first column contains ID, second IRR, rest of columns will hold cash flow for specific month.

Function should be able to process all columns instead of first 2 and store result in second column.

I know that I can get all columns from specific table with:

SELECT COLUMN_NAME 
FROM INFORMATION_SCHEMA.columns 
WHERE TABLE_NAME = 'First_Table'

Problems begin when I would like to create function that will return those columns as rows.

I can create function like so:

CREATE FUNCTION UnpivotRow (@TableName  varchar(50), @FromWhichColumn int, @Row int)
RETURNS @values TABLE
(
    id INT IDENTITY(0, 1),
    value DECIMAL(30, 10)
)
...

But how this function should look?

I think that ideal for this kind of processing table should look like so:

ProjectID    TimePeriod    Value
--------------------------------
        1             0      -10
        1             1        5
        2             0      -20
        2             1       10
        3             0     -100
        3             1      100
        4             0      -10
        4             1        0

I need to unpivot whole table without knowing number of columns.

---

EDIT:
If this can’t be done inside function, then maybe inside a procedure?

Answer 1

This can be done using dynamic SQL to perform the UNPIVOT:

DECLARE @cols AS NVARCHAR(MAX),
    @query  AS NVARCHAR(MAX),
    @colTP as  NVARCHAR(MAX)

select @cols = stuff((select ','+quotename(C.name)
         from sys.columns as C
         where C.object_id = object_id('table1') and
               C.name like 'M%'
         for xml path('')), 1, 1, '')


set @query = 'SELECT id, 
              replace(timeperiod, ''M'', '''') timeperiod, 
              value
              from table1
            unpivot 
            (
               value
               for timeperiod in (' + @cols + ')
            ) u '

exec(@query)

See SQL Fiddle with Demo.

This solution would have to be placed in a stored procedure.