houqp commented on a change in pull request #605:
URL: https://github.com/apache/arrow-datafusion/pull/605#discussion_r664706662
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File path: datafusion/src/logical_plan/plan.rs
##########
@@ -354,6 +356,43 @@ impl LogicalPlan {
| LogicalPlan::CreateExternalTable { .. } => vec![],
}
}
+
+ /// returns all `Using` join columns in a logical plan
+ pub fn using_columns(&self) -> Result<Vec<HashSet<Column>>,
DataFusionError> {
+ struct UsingJoinColumnVisitor {
+ using_columns: Vec<HashSet<Column>>,
+ }
+
+ impl PlanVisitor for UsingJoinColumnVisitor {
+ type Error = DataFusionError;
+
+ fn pre_visit(&mut self, plan: &LogicalPlan) -> Result<bool,
Self::Error> {
+ if let LogicalPlan::Join {
+ join_constraint: JoinConstraint::Using,
+ on,
+ ..
+ } = plan
+ {
+ self.using_columns.push(
+ on.iter()
+ .map(|entry| {
+ std::iter::once(entry.0.clone())
+ .chain(std::iter::once(entry.1.clone()))
Review comment:
i wanted to avoid an extra memory allocation incurred by `Vec::new`, but
i will double check to see if once chain is actually generating the optimal
code without memory allocations.
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