DECLARE @LikeCust char(2);
SET @LikeCust = 'C1';

WITH CustList
AS
(
	SELECT T1.Customer
	FROM LoanCustomer T1
		JOIN LoanCustomer T2
			ON T1.LOAN = T2.LOAN
	WHERE T1.Customer <> T2.Customer
		AND T2.Customer = @LikeCust
	GROUP BY T1.Customer
	-- Same number as @LikeCust
	HAVING COUNT(*) = (SELECT COUNT(*) FROM LoanCustomer WHERE Customer = @LikeCust)
	-- No more loans for T1
		AND COUNT(*) = (SELECT COUNT(*) FROM LoanCustomer T3 WHERE T3.Customer = T1.Customer)
)
SELECT T.LOAN, T.Customer
FROM LoanCustomer T
	JOIN CustList C
		ON T.Customer = C.Customer;

---------------------------------------------Create Table--------------------------------------------------------
CREATE TABLE LoanCustomer([KEY] INT,[LOAN] VARCHAR(10),[Customer] VARCHAR(10))
INSERT INTO LoanCustomer
SELECT 1,'L1','C5' UNION ALL
SELECT 2,'L2','C1' UNION ALL
SELECT 3,'L2','C2' UNION ALL
SELECT 4,'L3','C1' UNION ALL
SELECT 5,'L3','C2' UNION ALL
SELECT 6,'L4','C3' UNION ALL
SELECT 7,'L4','C4' UNION ALL
SELECT 8,'L5','C6' UNION ALL
SELECT 9,'L5','C7' UNION ALL
SELECT 10,'L6','C7' 

DECLARE @Cus VARCHAR(10)= 'C1'

SELECT * FROM LoanCustomer WHERE LOAN IN (SELECT Loan FROM LoanCustomer  WHERE  Customer=@Cus) AND Customer <>@Cus
---------------------------------------------Drop Table ----------------------------------------------------------
DROP TABLE LoanCustomer
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