[GitHub] [arrow-datafusion] HaoYang670 commented on issue #4191: scalar function `round` ignores second parameter

[GitBox <gi...@apache.org>]

HaoYang670 commented on issue #4191:
URL: https://github.com/apache/arrow-datafusion/issues/4191#issuecomment-1314694661

   Not sure, but I wonder could we support this is logical phase? 
   Given the following 2 lemmas:
   ```coq
   1. forall source: FloatArray, round(source) = round(source, 0)
   2. forall source: FloatArray n: IntArray,
           round(source, n) = div(
                                 round(mul(
                                         source, 
                                         pow(10, n))), 
                                 pow(10, n))
   ```
   we can unfold the `round` function in the logical plan stage and don't need to modify the physical stage.
   
   One concern here is that `Decimal` type might be better than `Float` type because we've found some corner cases in floating point multiplication and division:  


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