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Posted to github@datafusion.apache.org by "alamb (via GitHub)" <gi...@apache.org> on 2025/09/16 11:15:48 UTC

[I] Simplify `CASE WHEN false THEN ...` [datafusion]

alamb opened a new issue, #17590:
URL: https://github.com/apache/datafusion/issues/17590

   ### Is your feature request related to a problem or challenge?
   
   ### Is your feature request related to a problem or challenge?
   
   
   One form of Case statements look like
   ```sql
   CASE 
     WHEN <expr> THEN <expr>
     WHEN <expr> THEN <expr>
     ...
      ELSE
   END
   ```
   
   As suggested by @geoffreyclaude  in https://github.com/apache/datafusion/issues/17448#issuecomment-3293549174
   
   
   Any `WHEN false` will never execute and thus can be removed from the
   
   For example
   ```sql
   CASE 
     WHEN false THEN 1  -- never executed
     ELSE 2  
   END
   ```
   
   Could be simplified to 
   
   ```sql
   2
   ```
   
   Likewise
   
   ```sql
   CASE 
     WHEN x=y THEN 1 
     WHEN false THEN 2  -- never executed
     ELSE 3  
   END
   ```
   
   Could be simplified to 
   
   ```sql
   CASE 
     WHEN x=y THEN 1 
     ELSE 3  
   END
   ```
   
   
   ### Describe the solution you'd like
   
   I would like to implement the simplification above
   
   
   
   ### Describe alternatives you've considered
   
   I think we can just extend the existing rules for CASE simplification here:
   
   https://github.com/apache/datafusion/blob/ec4413e7d7b41c381c98eda909e5ab650be4c5e5/datafusion/optimizer/src/simplify_expressions/expr_simplifier.rs#L1398-L1400
   
   An example is In https://github.com/apache/datafusion/pull/17450 where @EeshanBembi implemented a new CASE simplification
   
   
   ### Additional context
   
   _No response_¯
   
   ### Describe the solution you'd like
   
   _No response_
   
   ### Describe alternatives you've considered
   
   _No response_
   
   ### Additional context
   
   _No response_


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Re: [I] Simplify `CASE WHEN false THEN ...` [datafusion]

Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb closed issue #17590: Simplify `CASE WHEN false THEN ...`
URL: https://github.com/apache/datafusion/issues/17590


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Re: [I] Simplify `CASE WHEN false THEN ...` [datafusion]

Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb commented on issue #17590:
URL: https://github.com/apache/datafusion/issues/17590#issuecomment-3297922071

   Since this is well specified and has an example PR I think it is a good first issue


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Re: [I] Simplify `CASE WHEN false THEN ...` [datafusion]

Posted by "SidChaudhary7 (via GitHub)" <gi...@apache.org>.
SidChaudhary7 commented on issue #17590:
URL: https://github.com/apache/datafusion/issues/17590#issuecomment-3299505982

   take


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