[GitHub] [arrow-datafusion] alamb commented on pull request #1729: Add median operator

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alamb commented on pull request #1729:
URL: https://github.com/apache/arrow-datafusion/pull/1729#issuecomment-1028915016


   > @alamb Am I missing something by any chance?
   
   I had a thought this morning: what if we didn't introduce an `Aggregate` function at all, and instead simply rewrote queries 
   
   so a query that has
   
   ```sql
   select approx_median(x) from foo;
   ```
   
   could be rewritten to 
   ```sql
   select approx_percentile(x, 5.0) as "approx_median(x)" from foo;
   ```
   
   Similar to how we transform `SELECT count(distinct x) from foo` to `select count(*) from (select x from foo group by x)` in https://github.com/realno/arrow-datafusion/blob/add-median-operator/datafusion/src/optimizer/single_distinct_to_groupby.rs#L44
   
   this may be a silly idea, but I wanted to write it down


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