-- *** Test Data ***
CREATE TABLE #temp
(
    CustID int NOT NULL
    ,PhoneID int NOT NULL
)
INSERT INTO #temp
SELECT 1, 10 UNION ALL
SELECT 2, 10 UNION ALL
SELECT 3, 11 UNION ALL
SELECT 1, 12 UNION ALL
SELECT 2, 12 UNION ALL
SELECT 4, 13 UNION ALL
SELECT 5, 11 UNION ALL
SELECT 5, 15 UNION ALL
SELECT 5, 18
-- *** End Test Data ***

CREATE TABLE #New2Old
(
    NewCustID int NOT NULL
    ,OldCustID int NOT NULL
    ,PRIMARY KEY (NewCustID, OldCustID)
)

;WITH PhoneDup (PhoneID, CustID)
AS
(
    SELECT T.PhoneID, T.CustID
    FROM #temp T
        JOIN (
                SELECT T1.PhoneID
                FROM #temp T1
                    JOIN #temp T2
                        ON T1.PhoneID = T2.PhoneID
                            AND T1.CustID <> T2.CustID
                GROUP BY T1.PhoneID
            ) D
            ON T.PhoneID = D.PhoneID
)
INSERT INTO #New2Old
SELECT DISTINCT
    ISNULL(V.CustID, T.CustID) AS NewCustID
    ,ISNULL(V.DupCustID, T.CustID) AS OldCustID
FROM #Temp T
    LEFT JOIN (
            SELECT D1.CustID, D2.CustID As DupCustID
            FROM PhoneDup D1
                JOIN PhoneDup D2
                    ON D1.PhoneID = D2.PhoneID
                        AND D1.CustID < D2.CustID
        ) V
        ON T.CustID = V.DupCustID

quote:

---

Originally posted by mattrigbye

ID CustID PhoneID
1    1        10
2    2        10
3    3        11
4    1        12
5    2        12
6    4        13
7    5        11
8    5        15
9    5        18

---