timsaucer commented on code in PR #24887:
URL: https://github.com/apache/datafusion/pull/24887#discussion_r3970774233
##########
datafusion/physical-expr/src/aggregate.rs:
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@@ -933,24 +933,44 @@ impl AggregateFunctionExpr {
/// For aggregates that do not support calculation in reverse,
/// returns None (which is the default value).
pub fn reverse_expr(&self) -> Option<AggregateFunctionExpr> {
+ self.reverse_expr_inner(false)
+ }
+
+ /// Same as [`Self::reverse_expr`], but the output `name` is always carried
+ /// over unchanged.
+ ///
+ /// Window execs derive their output schema from `WindowExpr::field()`,
which
+ /// for aggregate-backed window expressions is this expression's `name`. If
+ /// reversal renamed it, the rebuilt window exec would expose a differently
+ /// named column while parent plan nodes still reference the old one. This
+ /// mirrors `WindowUDFExpr::reverse_expr`, which preserves its name for the
+ /// same reason. `AggregateExec`, by contrast, pins its schema at
+ /// construction, so it can use [`Self::reverse_expr`] and let the name
+ /// reflect the function actually being evaluated.
+ pub fn reverse_expr_preserving_name(&self) ->
Option<AggregateFunctionExpr> {
Review Comment:
Great point! Thanks!
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