-- *** Test Data ***
DECLARE @CustomerPlans TABLE
(
    CustomerID int NOT NULL
    ,PlanType varchar(20) NOT NULL
    ,DateFrom datetime NOT NULL
    ,DateTo datetime NULL
)
INSERT INTO @CustomerPlans
SELECT 1, 'Basic', '20000101','20030601' UNION ALL
SELECT 1, 'Family', '20030601', NULL UNION ALL
SELECT 2, 'Family', '20020701', '20060314' UNION ALL
SELECT 3, 'Basic', '20000123','20040601' UNION ALL
SELECT 3, 'Family', '20040601','20070506' UNION ALL
SELECT 4, 'Basic', '20010823', NULL
-- *** End Test Data ***

SELECT C1.CustomerID
FROM @CustomerPlans C1
    JOIN @CustomerPlans C2
        ON C1.CustomerID = C2.CustomerID
WHERE C1.PlanType = 'Family'
    AND C2.PlanType = 'Basic'
    AND C2.DateTO <= C1.DateFrom
    AND C1.DateTo IS NOT NULL
    AND C2.DateTo IS NOT NULL