SQL with Manoj

–> Question:

I am trying to do update/insert operation using merge statement, but getting below 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.”

I am using SQL Server 2014. I knew there was a bug in older version of SQL Server (like version 2008). Does this issue still persist in latest version of SQL Server?
 

–> My Answer:
There might be 2 reasons:

1. Your source/target tables might be having DUPLICATES.

2. There might NO DUPLICATES, but you might be using NOLOCK hint? If yes, then your source table might be very big and going through constant changes (INSERT/UPDATE/DELETE), which might be causing PAGE-SPLITS and causing to read single source row TWICE. Try removing NOLOCK and run your MERGE stmt.
 

–> Another Answer by Naomi:

You need to fix the source of the problem, not apply patches. If your source has duplicate rows for the same key used to update, when how would you know which row will be used to update? The simple solution is to eliminate duplicates by either using correct combinations of keys to join or creating an extra key with ROW_NUMBER() approach.
 

Ref Link.