How to use GROUP BY clause in SQL MERGE statement?

Question

I am trying to join two tables, and I would like to use GROUP BY to fix the following error:

The MERGE statement attempted to UPDATE or DELETE the same row more than once. This happens when a target row matches more than one source row. A MERGE statement cannot UPDATE/DELETE the same row of the target table multiple times. Refine the ON clause to ensure a target row matches at most one source row, or use the GROUP BY clause to group the source rows.

Where exactly would the GROUP BY clause be?

 MERGE dbo.MyTarget targ USING dbo.MySource src ON (targ.Identifier = src.Identifier AND targ.Name = src.ConstituentName AND targ.Ticker = src.ConstituentTicker AND (targ.CUSIP = src.CUSIP OR targ.ISIN = src.ISIN OR targ.SEDOL = src.SEDOL)) WHEN MATCHED THEN -- update values ; 

Answer 1

Something like that:

 MERGE dbo.MyTarget targ USING (SELECT ... FROM dbo.MySource GROUP BY .....) src ON (targ.Identifier = src.Identifier AND targ.Name = src.ConstituentName AND targ.Ticker = src.ConstituentTicker AND (targ.CUSIP = src.CUSIP OR targ.ISIN = src.ISIN OR targ.SEDOL = src.SEDOL)) WHEN MATCHED THEN -- update values ;