declare @member table (Memberid int,Enrollmentdate datetime,Exitdate datetime)
insert @member
select 123, '2007-01-01', '2007-12-31' union all
select 123, '2008-01-01', '2008-12-31' union all
select 123, '2009-01-01', NULL  union all
select 234, '2007-01-01', NULL

declare @case table (memberid int, case_seq int,row_created datetime)
insert @case
select 123, 1, '2009-07-05' union all
select 234, 1, '2009-02-06'

SELECT b.memberid, 
       b.case_seq, 
       b.row_created, 
       a.Enrollmentdate, 
       a.Exitdate 
FROM   (SELECT *, 
               row_number() 
                 OVER(PARTITION BY Memberid ORDER BY Exitdate) AS rn 
        FROM   @member) a 
       INNER JOIN @case b 
         ON a.Memberid = b.memberid 
WHERE  a.rn = 1