[GitHub] [arrow-datafusion] Dandandan opened a new issue #566: Common subexpression elimination

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

Dandandan opened a new issue #566:
URL: https://github.com/apache/arrow-datafusion/issues/566


   **Is your feature request related to a problem or challenge? Please describe what you are trying to do.**
   I like to support eliminating common subexpressions from a query plan.
   
   For example, this example from TCP-H query 1:
   ```sql
   select *
       sum(l_extendedprice * (1 - l_discount)) as sum_disc_price,
       sum(l_extendedprice * (1 - l_discount) * (1 + l_tax)) as sum_charge
   from T
   ```
   could be rewritten to reuse the result of `l_extendedprice * (1 - l_discount)` by moving it into another projection.
   This looks in SQL as something like:
   
   ```sql
   with temp as (
      select
          l_extendedprice * (1 - l_discount) as cs
      from t
   )
   select 
       sum(cs) as sum_disc_price,
       sum(cs * (1 + l_tax)) as sum_charge
   from temp
   ```
   
   **Describe the solution you'd like**
   Detect common subexpression in projections / group by, join conditions etc. and remove them by moving doing them once in a projection step. Note: this only makes sense when the expression includes any calculation (e.g. not a column reference with alias).
   
   **Describe alternatives you've considered**
   n/a
   **Additional context**
   n/a


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[GitHub] [arrow-datafusion] alamb closed issue #566: Common subexpression elimination

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

alamb closed issue #566:
URL: https://github.com/apache/arrow-datafusion/issues/566


   


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