[jira] [Commented] (ARROW-15590) [C++] Add support for joins to the Substrait consumer

["Vibhatha Lakmal Abeykoon (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-15590?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17530074#comment-17530074 ] 

Vibhatha Lakmal Abeykoon commented on ARROW-15590:
--------------------------------------------------

While looking into Substrait-Join integration, I observed that, the Substrait spec provides the following properties for a join operation.

- Left Input 
- Right Input
- Join Expression
- Join Type


While in Arrow API, the HashJoinOptions are (minimum options)


- left keys
- right keys
- join type


To translate the Substrait inputs and obtain left and right keys, is there a way to extract the `FieldPath` from an expression? 
We are not supporting experssions on join-key, right? AFAIK there is only a filter expression available. Please correct me if I am on a wrong path.

cc [~westonpace] [~lidavidm] 

> [C++] Add support for joins to the Substrait consumer
> -----------------------------------------------------
>
>                 Key: ARROW-15590
>                 URL: https://issues.apache.org/jira/browse/ARROW-15590
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: C++
>            Reporter: Weston Pace
>            Assignee: Vibhatha Lakmal Abeykoon
>            Priority: Major
>              Labels: substrait
>
> The streaming execution engine supports joins.  The Substrait consumer does not currently consume joins.  We should add support for this.  We may want to split this PR into subtasks as there are many different kinds of joins and we may not support all of them immediately.



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