[GitHub] [arrow-datafusion] houqp commented on a change in pull request #778: JOIN conditions are order dependent

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

houqp commented on a change in pull request #778:
URL: https://github.com/apache/arrow-datafusion/pull/778#discussion_r677152935



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File path: datafusion/src/logical_plan/builder.rs
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@@ -282,14 +282,28 @@ impl LogicalPlanBuilder {
             ));
         }
 
-        let left_keys: Vec<Column> = left_keys
-            .into_iter()
-            .map(|c| c.into().normalize(&self.plan))
-            .collect::<Result<_>>()?;
-        let right_keys: Vec<Column> = right_keys
-            .into_iter()
-            .map(|c| c.into().normalize(right))
-            .collect::<Result<_>>()?;
+        let (left_keys, right_keys): (Vec<Result<Column>>, Vec<Result<Column>>) =

Review comment:
       Yeah, I think the argument name makes sense with the old assumption that left_keys should only refer to columns from the left plan. With this fix, it can become confusing.
   
   Perhaps a better signature for this function would be something along the lines of: `join_keys: Vec<(impl Into<Column>, impl Into<Column>)>`.
   
   If we want the dataframe API to also support order independent JOIN conditions, then it is indeed better to address the fix within this builder method. Otherwise I agree it would be better to fix it in the SQL planner instead. I am leaning towards supporting this in dataframe API as well.




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