Something like this

DECLARE@tbl_Customer TABLE

(

Customer_idINT,

ValueNUMERIC(18,2)

)

DECLARE@tbl_Relation TABLE

(

Customer_idINT,

Child_idINT

)

INSERT@tbl_Customer

SELECT1, 100 UNION ALL

SELECT2, 150 UNION ALL

SELECT3, 1000 UNION ALL

SELECT4, 300 UNION ALL

SELECT10, 120 UNION ALL

SELECT11, 150 UNION ALL

SELECT12, 1000 UNION ALL

SELECT13, 200

INSERT@tbl_Relation

SELECT1, 10 UNION ALL

SELECT1, 11 UNION ALL

SELECT1, 12 UNION ALL

SELECT2, 13 UNION ALL

SELECT3, 14 UNION ALL

SELECT3, 15 UNION ALL

SELECT5, 16

SELECTC.Customer_id, C.Value + COALESCE( SUM( CR.Value ), 0 ) AS Value

FROM@tbl_Customer AS C

LEFT OUTER JOIN@tbl_Relation AS R ON C.Customer_id = R.Customer_id

LEFT OUTER JOIN @tbl_Customer AS CR ON R.Child_id = CR.Customer_id

GROUP BY C.Customer_id, C.Value

ORDER BY C.Customer_id