If you really want to get crazy, here's a solution:
SELECT [FieldA], [FieldB], a.[FieldC], [FieldD], [FieldE]
FROM [TABLE] a
LEFT JOIN(
SELECT DISTINCT [FieldC], pwdencrypt([FieldC]) as [FieldE]
FROM [TABLE]) b
ON a.[FieldC] = b.[FieldC]
That pwdencrypt()
creates a very unique id.