[GitHub] [druid] clintropolis commented on issue #9412: Regression: SQL query with multiple similar CASE clauses cannot be translated to correct native json format

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clintropolis commented on issue #9412: Regression: SQL query with multiple similar CASE clauses cannot be translated to correct native json format
URL: https://github.com/apache/druid/issues/9412#issuecomment-591674647
 
 
   Thanks for the report, it looks like a couple of things are going on here.
   
   I think the new in 0.17 behavior is that _both_ of the expressions are being optimized into "true", my guess calcite optimizing something due to SQL lack of null equivalence means only the else is possible. I haven't confirmed yet, but I suspect #8566 might be related.
   
   Try this instead:
   
   ```
   SELECT 
   	CASE WHEN cityName IS NULL THEN FALSE ELSE TRUE END AS col_a,
   	CASE WHEN countryName IS NULL THEN FALSE ELSE TRUE END AS col_b
   FROM wikipedia
   GROUP BY 1, 2
   ```
    
   Anyway, the optimization calcite was doing uncovers another bug, which I think might be caused by the changes of #6902, which refactored druid sql to re-use virtual columns for the same expressions, but this appears to make grouping sad if both columns that are now the same virtual column are being grouped on.

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