[I] [docs] Fix incorrect null value syntax in aggregation merge engine examples [fluss]

["platinumhamburg (via GitHub)" <gi...@apache.org>]

platinumhamburg opened a new issue, #2644:
URL: https://github.com/apache/fluss/issues/2644

   ### Search before asking
   
   - [x] I searched in the [issues](https://github.com/apache/fluss/issues) and found nothing similar.
   
   
   ### Description
   
   The documentation examples for last_value, last_value_ignore_nulls, and first_value_ignore_nulls aggregate functions use direct null literals in INSERT INTO ... VALUES statements:
   ```
   INSERT INTO test_last_value_ignore_nulls VALUES
       (1, 'user@example.com', '123-456'),
       (1, null, '789-012'),  -- Direct null literal
       (1, 'new@example.com', null);
   ```
   When users try to execute these examples, Flink SQL throws a validation error:
   ```
   org.apache.flink.table.api.ValidationException: SQL validation failed. 
   From line 1, column 77 to line 1, column 80: Illegal use of 'NULL'
   ```
   Because that the Flink SQL does not support direct null literals in INSERT INTO ... VALUES statements due to type inference limitations. The SQL parser cannot determine the data type of a bare null value.
   
   ### Willingness to contribute
   
   - [ ] I'm willing to submit a PR!


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Re: [I] [docs] Fix incorrect null value syntax in aggregation merge engine examples [fluss]

["swuferhong (via GitHub)" <gi...@apache.org>]

swuferhong closed issue #2644: [docs] Fix incorrect null value syntax in aggregation merge engine examples
URL: https://github.com/apache/fluss/issues/2644


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