Here is another approach not using JOIN.
SELECTGUID,
MIN(TableName) AS TableName
FROM(
SELECTGUID,
'TableA' AS TableName
FROMTableA
UNION ALL
SELECTGUID,
'TableB'
FROMTableB
UNION ALL
SELECTGUID,
'TableC'
FROMTableC
) AS d
GROUP BYGUID
HAVINGCOUNT(*) = 1
N 56°04'39.16"
E 12°55'05.25"