alamb commented on code in PR #8169:
URL: https://github.com/apache/arrow-datafusion/pull/8169#discussion_r1393420890
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datafusion/physical-expr/src/equivalence.rs:
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@@ -575,10 +588,13 @@ impl OrderingEquivalenceClass {
}
}
- /// Gets the first ordering entry in this ordering equivalence class.
- /// This is one of the many valid orderings (if there are multiple).
+ /// Returns the concatenation of all the orderings. This enables merge
+ /// operations to preserve all equivalent orderings simultaneously.
pub fn output_ordering(&self) -> Option<LexOrdering> {
- self.orderings.first().cloned()
+ let output_ordering =
+ self.orderings.iter().flatten().cloned().collect::<Vec<_>>();
+ let output_ordering = collapse_lex_ordering(output_ordering);
Review Comment:
this is another core change, right? It preserves all the possible orderings
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