waynexia opened a new pull request, #3305:
URL: https://github.com/apache/arrow-datafusion/pull/3305

   Signed-off-by: Ruihang Xia <[email protected]>
   
   # Which issue does this PR close?
   
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   Closes #2994.
   
    # Rationale for this change
   <!--
    Why are you proposing this change? If this is already explained clearly in 
the issue then this section is not needed.
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   The original issue is https://github.com/CeresDB/ceresdb/issues/59, and a 
minimal reproducer can be found in #2994.
   
   This is trying to fix the `single_distinct_to_groupby` optimizer cannot 
handle a `GROUP BY` with an expression, like `GROUP BY c+1`. To fix this, we 
need to alias the "original" GROUP BY in the subquery and refer to that aliased 
column in outer. E.g.:
   ```sql
   Before optimize
   SELECT id+1, count(distinct(bank_account))
   FROM users
   GROUP BY id+1;
   ```
   After optimize
   ```sql
   SELECT group_by_alias1 as "id+1", count(bank_account)
   FROM (
     SELECT id+1 as group_by_alias1, bank_account
     FROM users 
     GROUP BY id+1, bank_account
   )
   GROUP BY group_by_alias1;
   ```
   # What changes are included in this PR?
   <!--
   There is no need to duplicate the description in the issue here but it is 
sometimes worth providing a summary of the individual changes in this PR.
   -->
   
   - alias `group_by` exprs
   - rename some symbols and add comment
   - a test to cover this case `group_by_with_expr`
   
   # Are there any user-facing changes?
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updated before approving the PR.
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   No
   <!--
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