siwen-yu opened a new issue, #11729:
URL: https://github.com/apache/seatunnel/issues/11729

   ### Search before asking
   
   - [X] I had searched in the 
[issues](https://github.com/apache/seatunnel/issues) and found no similar 
issues.
   
   ### What happened
   
   When using JDBC connectors for databases that rely on the `MERGE ... WHEN 
MATCHED THEN UPDATE SET` upsert syntax (DM, Oracle, SAP HANA, SQL Server, 
Vertica, Xugu), upserting into a table whose **every column is a primary/unique 
key** (i.e. there is no non-key field to update) fails.
   
   The generated upsert SQL always appends `WHEN MATCHED THEN UPDATE SET 
<clause>`. When `updateSetClause` is empty, this produces invalid SQL (`UPDATE 
SET` with an empty body), and the database throws a syntax error, causing the 
job to fail.
   
   ### SeaTunnel Version
   
   2.3.13 (and dev branch)
   
   ### Connector Name
   
   jdbc — dm, oracle, saphana, sqlserver, vertica, xugu
   
   ### What you expected to happen
   
   When there is nothing to update, the `WHEN MATCHED THEN UPDATE SET` clause 
should be omitted entirely, so the MERGE statement is valid and the job 
succeeds (matched rows are left unchanged, unmatched rows are inserted).
   
   ### How to reproduce
   
   1. Create a table whose all columns are primary keys, e.g.:
      ```sql
      CREATE TABLE all_key_t (a INT PRIMARY KEY, b INT PRIMARY KEY);
      ```
   2. Configure a SeaTunnel JDBC sink (dm / oracle / saphana / sqlserver / 
vertica / xugu) with an upsert mode and run a job that writes/updates multiple 
rows.
   3. Observe the SQL syntax error thrown by the database (empty `UPDATE SET`).
   
   ### Anything else
   
   A fix is provided in the linked PR.
   


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