buraksenn commented on code in PR #20926:
URL: https://github.com/apache/datafusion/pull/20926#discussion_r3040198754
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datafusion/physical-plan/src/aggregates/mod.rs:
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@@ -1113,6 +1163,34 @@ impl AggregateExec {
}
}
+ /// Computes the estimated number of distinct groups across all grouping
sets.
+ /// For each grouping set, computes `product(NDV_i + null_adj_i)` for
active columns,
+ /// then sums across all sets. Returns `None` if any active column is not
a direct
+ /// column reference or lacks `distinct_count` stats.
+ /// When `null_count` is absent or unknown, null_adjustment defaults to 0.
+ fn compute_group_ndv(&self, child_statistics: &Statistics) ->
Option<usize> {
Review Comment:
I think this makes sense but to not overcomplicate compute_group_ndv I've
extracted `estimate_num_rows` from the caller side to wrap this. Hope it is ok
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