Question

To keep it simple, my question is similar to THIS QUESTION, PART 2, only problem is, I am not running Oracle and thus can not use the rownumbers.

For those who need more information and examples:

I have a table

  contractId date          value    
  1          09/02/2011     A         
  1          13/02/2011     C          
  2          02/02/2011     D   
  2          08/02/2011     A  
  2          12/02/2011     C  
  3          22/01/2011     C  
  3          30/01/2011     B  
  3          12/02/2011     D    
  3          21/01/2011     A

EDIT: added another line for ContractID. Since I had some code myself, but that would display the following:

  contractId date          value    value_old
  1          09/02/2011     A                  
  2          08/02/2011     A         D
  3          30/01/2011     B         C    
  3          30/01/2011     B         A 

But that is not what I want ! The result should still be as below!

Now I want to select the last record before a given date and compare that with the previous value.
Suppose the ‘given date’ is 11/02/2011 in this example, the output should be like this:

  contractId date          value    value_old
  1          09/02/2011     A                  
  2          08/02/2011     A         D
  3          30/01/2011     B         C    

I do have the query to select the last record before the given date. That is the easy part. But to select the last record before that, I am lost…

I really hope I can get some help here, have been breaking my head over this for days and looking for answers on the web and stackoverflow.

Answer 1

One possibility:

SELECT a.contractId, a.Date, a.Value, (SELECT Top 1 b.[Value] 
        FROM tbl b 
        WHERE b.[Date] < a.[Date] And b.ContractID=a.ContractID
        ORDER BY b.[Date] Desc) AS Old_Value
FROM tbl AS a
WHERE a.Date IN 
       (SELECT TOP 1 b.Date 
        FROM tbl b 
        WHERE b.ContractID=a.ContractID
        AND b.Date < #2011/02/11#
        ORDER BY b.date DESC)