• -- Have a look at the dupesets in the source table - do you want them, or not?

    -- Then decide what to do. No point in finding a clever way to

    -- insert the dupes if you don't want them.

    SELECT *

    FROM (

    SELECT

    *,

    Dupecount = COUNT(*) OVER(PARTITION BY ASSETDETAIL_Id, ASSET_UDF_DESC)

    FROM [RawData_AssetClassUDF]

    ) d

    WHERE Dupecount > 1

    ORDER BY ASSETDETAIL_Id, ASSET_UDF_DESC

    “Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw

    For fast, accurate and documented assistance in answering your questions, please read this article.
    Understanding and using APPLY, (I) and (II) Paul White
    Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden