One way...

SELECT *

FROM

(SELECT DDid

, Seq

, Descrip

, ROW_NUMBER() OVER (PARTITION BY DDid, Seq ORDER BY DDid, Seq) AS rn

FROM

(SELECT 1 As DDid, 0 AS Seq, 'AAA' AS Descrip

UNION ALL

SELECT 1, 1, 'BBB'

UNION ALL

SELECT 2, 0, 'YYY'

UNION ALL

SELECT 2, 1, 'XXX'

UNION ALL

SELECT 2, 2, 'QQQ'

UNION ALL

SELECT 2, 2, 'WWW'

UNION ALL

SELECT 2, 3, 'RRR') data ) x

WHERE x.rn>1

Another:

SELECT DDID, Seq, COUNT(Descrip)

FROM

(SELECT 1 As DDid, 0 AS Seq, 'AAA' AS Descrip

UNION ALL

SELECT 1, 1, 'BBB'

UNION ALL

SELECT 2, 0, 'YYY'

UNION ALL

SELECT 2, 1, 'XXX'

UNION ALL

SELECT 2, 2, 'QQQ'

UNION ALL

SELECT 2, 2, 'WWW'

UNION ALL

SELECT 2, 3, 'RRR') data

GROUP BY DDID, Seq

HAVING COUNT(Descrip)>1;