neilconway commented on code in PR #22718:
URL: https://github.com/apache/datafusion/pull/22718#discussion_r3345630536
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datafusion/physical-plan/src/filter.rs:
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@@ -861,15 +894,56 @@ fn interval_bound_to_precision(
}
}
-/// This function ensures that all bounds in the `ExprBoundaries` vector are
-/// converted to closed bounds. If a lower/upper bound is initially open, it
-/// is adjusted by using the next/previous value for its data type to convert
-/// it into a closed bound.
+/// Scales a column's `byte_size` by the estimated filter `selectivity`. An
+/// exact zero is preserved: an empty column stays exactly empty after
+/// filtering.
+fn scale_byte_size(byte_size: Precision<usize>, selectivity: f64) ->
Precision<usize> {
+ match byte_size {
+ Precision::Exact(0) => Precision::Exact(0),
+ byte_size => byte_size.with_estimated_selectivity(selectivity),
+ }
+}
+
+/// Caps a row-bounded column statistic (a null count or distinct count) at the
+/// filtered row estimate, since a column cannot have more nulls or distinct
+/// values than it has rows. Known counts are demoted to inexact because the
+/// filtered row count is itself an estimate.
+fn cap_at_rows(
+ value: Precision<usize>,
+ filtered_num_rows: Precision<usize>,
+) -> Precision<usize> {
+ match filtered_num_rows {
+ Precision::Absent => value.to_inexact(),
+ rows => value.to_inexact().min(&rows),
+ }
+}
+
+/// Returns the NDV for a column constrained to one non-null value, such as
+/// `column = literal` or a singleton interval. The constraint gives NDV at
+/// most one; a zero-row output has no distinct values.
+///
+/// The caller is responsible for proving the singleton domain.
+fn distinct_count_for_singleton_domain(
+ filtered_num_rows: Precision<usize>,
+) -> Precision<usize> {
+ match filtered_num_rows {
+ Precision::Exact(0) | Precision::Inexact(0) => filtered_num_rows,
+ _ => Precision::Exact(1),
Review Comment:
Makes sense, done.
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