Question

I have this simple problem in SQL. I have a table with 4 columns. Columns being ID, DateTime, Decimal, AnotherID.

DECLARE @data DATETIME 
SET @data = '20120101'

SELECT [ID]
      ,[Data]
      ,[Value]
      ,[InID]   
 FROM [dbo].[Static] 
 WHERE InID = 1 AND [Data] <= @data

Now I have to choose proper Value based on InID and Data. InID can have multiple rows with different dates. This is example output for InID = 1.

ID          Data            Value              InID
389         2012-01-02      10.00000000     1
390         2011-12-16      20.00000000     1
391         2011-12-13      15.00000000     1

Now based on InID and Data I need to get Value for given date. For example for InID = 1 I need to get Value for day 2011-12-14. Of course the value should be taken from 13th of December and if I ask it about value for date 2012-01-13 it should take last value. However in case the question is about date before the first date it should return NULL. I tried multiple combinations but my brain seems to be out of order atm so any help would be appreciated.

Answer 1

Try this to get only the most recent Value constrained by the @data parameter:

SELECT TOP 1 [Value]
FROM [dbo].[Static] 
WHERE InID = 1 AND [Data] <= @data
ORDER BY [Data] DESC;

To the last part of your question if you need a NULL result you’ll have to wrap the query above as it will return an empty result set if nothing qualifies:

DECLARE @theValue float;
SELECT @theValue = (
  SELECT TOP 1 [Value]
  FROM [dbo].[Static] 
  WHERE InID = 1 AND [Data] <= @data
  ORDER BY [Data] DESC
);

The nearest would be this (just be aware that it can grab either future or past dates):

 SELECT TOP 1 [Value]
 FROM [dbo].[Static]
 WHERE InID = 1
 ORDER BY ABS(DATEDIFF(Day, [Data], @data));