[GitHub] [arrow-datafusion] alamb opened a new issue #417: Implement constant folding for CAST

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

alamb opened a new issue #417:
URL: https://github.com/apache/arrow-datafusion/issues/417


   **Is your feature request related to a problem or challenge? Please describe what you are trying to do.**
   When pushing predicates down into various storage systems, it is common for them to support single column predicates of the form
   
   ```
   const OP column
   ```
   
   SQL allows users to write predicates against columns using whatever format they deem useful, and inserts the appropriate `CAST` functions where needed.
   
   However
   
   ```
   echo "1" > /tmp/foo.csv
   cargo run -p datafusion-cli
   ```
   And then run:
   ```
   > CREATE EXTERNAL TABLE foo(ts double)
   STORED AS CSV
   LOCATION '/tmp/foo.csv';
   0 rows in set. Query took 0 seconds.
   > explain verbose select * from foo where ts < 5;
   +-----------------------------------------+--------------------------------------------------------------------------+
   | plan_type                               | plan                                                                     |
   +-----------------------------------------+--------------------------------------------------------------------------+
   | logical_plan                            | Projection: #ts                                                          |
   |                                         |   Filter: #ts Lt Int64(5)                                                |
   |                                         |     TableScan: foo projection=None                                       |
   | logical_plan after projection_push_down | Projection: #ts                                                          |
   |                                         |   Filter: #ts Lt Int64(5)                                                |
   |                                         |     TableScan: foo projection=Some([0])                                  |
   | logical_plan after projection_push_down | Projection: #ts                                                          |
   |                                         |   Filter: #ts Lt Int64(5)                                                |
   |                                         |     TableScan: foo projection=Some([0])                                  |
   | physical_plan                           | ProjectionExec: expr=[ts]                                                |
   |                                         |   FilterExec: ts < CAST(5 AS Float64)                                    |
   |                                         |     CsvExec: source=Path(/tmp/foo.csv: [/tmp/foo.csv]), has_header=false |
   +-----------------------------------------+--------------------------------------------------------------------------+
   4 rows in set. Query took 0 seconds.
   ```
   
   You can see that the filter that was pushed down was `ts < CAST(5 AS Float64)  ` which is correct, but it will likely not be recognized by some storage systems (such as IOx).
   
   
   **Describe the solution you'd like**
   What I would like to see is the expression rewriter pass rewrite `ts < CAST(5 AS Float64)` into `ts < 5.0` (aka do the cast at plan time)
   


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[GitHub] [arrow-datafusion] jorgecarleitao closed issue #417: Implement constant folding for CAST

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

jorgecarleitao closed issue #417:
URL: https://github.com/apache/arrow-datafusion/issues/417


   


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