Question

I have a table with data like so:

ID    StartDate    EndDate     EffectiveDate
--    ---------    -------     -------------
1     1/1/2009     12/31/2009    12/31/2009
1     7/1/2009     12/31/2009    7/1/2009
1     8/1/2009     12/31/2009    8/1/2009
2     1/1/2010     12/31/2010    12/31/2010
2     3/1/2010     12/31/2010    12/31/2010

I need a query that will format it like this, however:

ID    StartDate    EndDate     EffectiveDate
--    ---------    -------     -------------
1     1/1/2009     6/30/2009    null
1     7/1/2009     7/31/2009    7/1/2009
1     8/1/2009     12/31/2009   8/1/2009
2     1/1/2010     2/28/2010    null
2     3/1/2010     12/31/2010   12/31/2010
...

It’s basically like a timeline with segmented “points”, and each point is a new StartDate with an EndDate of the next point, and so on.

I’ve tried using a CTE, as well as the following query:

   SELECT t1.RfqItemOptionId, 
          t1.StartDate, 
          MIN(t2.EffectiveDate) EndDate,  
          t1.EffectiveDate EffectiveDate
     FROM @OptionPeriods t1 
LEFT JOIN @OptionPeriods t2 ON t1.RfqItemOptionId = t2.RfqItemOptionId
                           AND t1.EffectiveDate < t2.EffectiveDate
 GROUP BY t1.RfqItemOptionId, t1.StartDate, t1.EffectiveDate

Which is close…but no cigar 🙁

Can anyone help?

Answer 1

;With Base As
(
    Select
          *
        , ROW_NUMBER() Over (Partition By ID Order By StartDate) RowNum
    From
        @OptionPeriods
)
Select
      B1.*
    , IsNull(B2.StartDate - 1, B1.EndDate) As NewEndDate
    , Case B1.RowNum When 1 then Null Else B1.StartDate End As NewEffectiveDate
From
    Base B1
Left Join
    Base B2
On
    B1.ID = B2.ID
    AND
    B1.RowNum + 1 = B2.RowNum