question

In my situation, I want to extract Start Date and Stop Date from following table as you can see i have only 1 Date column which contain Start/Change/Stop Date which depends on ACTION column : 01 - Start (New drug start) 02 - Change (Change of dose) 03 - Stop ( Drug Stopped) The tricky bit is that When Action=02 dose is changed so the Change date should become Start date for the current dose and stop date for the previouse dose. I am really confused with it,, CREATE TABLE TEST(ID VARCHAR(10), [TherapyAction] INT, [Drug] INT, [Dose] FLOAT, [TherapyDate] DATETIME) INSERT INTO [dbo].[TEST] VALUES ('XXX' ,1, 1, 60, '01/09/2009 '), ('57A' ,3, 1, 60, '09/07/2011'), ('57A' ,1, 3, 5, '25/06/2010'), ('57A' ,3, 3, 5, '09/07/2011' ), ('57A' ,1, 4, 187.5, '19/02/2010'), ('57A' ,2, 4, 250, '01/06/2010' ), ('57A' ,3, 4, 250, '09/07/2011' ), ('A5B' ,1, 1, 12.5, '26/01/2007' ), ('A5B' ,2, 1, 25, '06/02/2007' ), ('A5B' ,2, 1, 225, '20/08/2009'), ('A5B' ,1, 4, 62.5, '04/07/2006'), ('A5B' ,2, 4, 125, '12/07/2006'), ('A5B' ,2, 4, 250, '01/05/2008'), ('A5B' ,1, 7, 7.5, '11/09/2006'), ('A5B' ,3, 7, 7.5, '26/01/2007'), ('A5B' ,1, 7, 9, '09/04/2010'), ('A5B', 3, 7, 9, '19/07/2010') SELECT * FROM [dbo].[TEST] Any help will be greatly appreciated