There are several ways to do acheive the same...

Here is the simple/basic query which strikes to my mind immediately

SELECT A.ClaimKey,

CASE WHEN A.MinClaim > B.MinClaim THEN 'Y' ELSE 'N' END AS YesOrNoBefore,

CASE WHEN A.MinClaim > B.MinClaim THEN 'N' ELSE 'Y' END AS YesOrNoAfter

FROM

(

SELECT ClaimKey, MIN(ClaimSequenceNumber) MinClaim

FROM TESTTABLE

WHERE YesOrNo='N'

GROUP BY ClaimKey

)A

,

(

SELECT ClaimKey, MIN(ClaimSequenceNumber) MinClaim

FROM TESTTABLE

WHERE YesOrNo='Y'

GROUP BY ClaimKey

)B

WHERE

A.ClaimKey = B.ClaimKey