SELECT t1.REPORT_ID,
t1.data
FROM (
SELECT DISTINCT A.REPORT_ID,
stuff(( SELECT DISTINCT '' + B.REPORT_EL_ID
FROM REPORT_DAT B
WHERE A.REPORT_ID = B.REPORT_ID
FOR XML PATH(''), TYPE).value('.', 'NVARCHAR(MAX)'),1,0,'') AS data
FROM REPORT_DAT A
) t1
INNER JOIN (
SELECT DISTINCT A.REPORT_ID,
stuff(( SELECT DISTINCT '' + B.REPORT_EL_ID
FROM REPORT_DAT B
WHERE A.REPORT_ID = B.REPORT_ID
FOR XML PATH(''), TYPE).value('.', 'NVARCHAR(MAX)'),1,0,'') AS data
FROM REPORT_DAT A
) t2
ON t1.data = t2.data
AND t1.REPORT_ID != t2.REPORT_ID
ORDER BY t1.REPORT_ID