Try this
DECLARE @T TABLE(ID_NO INT IDENTITY,FIRST_NAME VARCHAR(50), LAST_NAME VARCHAR(50))
INSERT INTO @T VALUES('X','ABC'),('Y','ABC'),('M','PQR'),('N','PQR')
--SELECT * FROM @T
;WITH CTE AS(
SELECT
Rn = ROW_NUMBER() OVER(PARTITION BY t2.LAST_NAME ORDER BY (SELECT 1))
,t2.LAST_NAME
+ ',' +
STUFF(( SELECT '-' + t1.FIRST_NAME
FROM @T t1
WHERE t1.LAST_NAME = t2.LAST_NAME
FOR XML PATH(''),TYPE) .value('.','NVARCHAR(MAX)'),1,1,'')AS Concat_FirstName
FROM @T t2
)
SELECT
STUFF(( SELECT '/' + c1.Concat_FirstName
FROM CTE c1
WHERE c1.Rn = c2.Rn
FOR XML PATH(''),TYPE)
.value('.','NVARCHAR(MAX)'),1,1,'') AS Concat_FirstName
FROM CTE c2 WHERE Rn= 1
GROUP BY c2.Rn
Result Concat_FirstName ABC,X-Y/PQR,M-N Hope this helps
