try this:

DECLARE @a as TABLE(Eid VARCHAR(5),DocNo VARCHAR(5))

DECLARE @b-2 as TABLE(Cid VARCHAR(5),CDocNo VARCHAR(5))

DECLARE @C as TABLE(Did VARCHAR(5),EDocNo VARCHAR(5))

INSERT INTO @a

VALUES

('a','1'), ('a','2'),('a','4'), ('a','6'), ('c','3'), ('b','4'), ('e','5'),

('b','1'), ('b','3'), ('b','6')

INSERT INTO @b-2

VALUES

('a','1'), ('a','2'), ('b','4')

-- Solution1:

SELECT x.Eid AS Eid

, b.cDocNo AS cDocNo

FROM @b-2 b RIGHT JOIN ( SELECT A.Eid

, A.DocNo

FROM @a a INNER JOIN @b-2 b ON ( A.Eid = b.cid )

GROUP BY A.Eid

, A.DocNo ) x ON ( ( b.Cid = x.Eid )

AND ( b.CDocNo = x.DocNo ))

ORDER BY x.Eid

-- Solution2:

INSERT INTO @C

SELECT A.Eid

, A.DocNo

FROM @a a INNER JOIN @b-2 b ON ( A.Eid = b.cid )

GROUP BY A.Eid

, A.DocNo

SELECT c.Did AS Eid

, b.cDocNo AS cDocNo

FROM @C c LEFT JOIN @b-2 b ON ( ( C.Did = b.cid )

AND ( C.EDocNo = b.CDocNo ))

ORDER BY C.Did