ozankabak commented on code in PR #5035:
URL: https://github.com/apache/arrow-datafusion/pull/5035#discussion_r1090123476
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datafusion/core/src/physical_plan/union.rs:
##########
@@ -220,55 +220,55 @@ impl ExecutionPlan for UnionExec {
}
fn output_ordering(&self) -> Option<&[PhysicalSortExpr]> {
- let first_input_ordering = self.inputs[0].output_ordering();
- // If the Union is not partition aware and all the input ordering spec
strictly equal with the first_input_ordering
- // Return the first_input_ordering as the output_ordering
- //
- // It might be too strict here in the case that the input ordering are
compatible but not exactly the same.
- // For example one input ordering has the ordering spec
SortExpr('a','b','c') and the other has the ordering
- // spec SortExpr('a'), It is safe to derive the out ordering with the
spec SortExpr('a').
- if !self.partition_aware
- && first_input_ordering.is_some()
- && self
- .inputs
- .iter()
- .map(|plan| plan.output_ordering())
- .all(|ordering| {
- ordering.is_some()
- && sort_expr_list_eq_strict_order(
- ordering.unwrap(),
- first_input_ordering.unwrap(),
- )
- })
- {
- first_input_ordering
+ // If the Union is partition aware, there is no output ordering.
+ // Otherwise, the output ordering is the "meet" of its input orderings.
+ // The meet is the finest ordering that satisfied by all the input
+ // orderings, see https://en.wikipedia.org/wiki/Join_and_meet.
+ if self.partition_aware {
+ return None;
+ }
+ // To find the meet, we first find the smallest input ordering.
+ let mut smallest: Option<&[PhysicalSortExpr]> = None;
Review Comment:
Thanks for double checking, will open a PR shortly 👍
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