mdashti commented on code in PR #23106:
URL: https://github.com/apache/datafusion/pull/23106#discussion_r3470181133
##########
datafusion/physical-plan/src/joins/hash_join/shared_bounds.rs:
##########
@@ -685,12 +699,49 @@ impl SharedBuildAccumulator {
)?) as Arc<dyn PhysicalExpr>
};
- self.dynamic_filter.update(filter_expr)?;
+ self.dynamic_filter
+ .update(self.preserve_probe_nulls(filter_expr))?;
}
}
Ok(())
}
+
+ /// Keeps probe rows with a NULL key when the join semantics need them.
+ ///
+ /// The build-side predicate drops probe rows whose key is NULL. A
null-aware anti join
+ /// (`NOT IN`) needs that NULL to reach the join so three-valued logic can
collapse the
+ /// result, and a null-equal join needs it to match a build-side NULL.
OR-ing `key IS NULL`
+ /// keeps those rows while preserving the filter's selectivity for the
rest; the join refines
+ /// whatever the widened filter lets through.
+ fn preserve_probe_nulls(
+ &self,
+ filter_expr: Arc<dyn PhysicalExpr>,
+ ) -> Arc<dyn PhysicalExpr> {
+ if self.null_equality != NullEquality::NullEqualsNull &&
!self.null_aware {
+ return filter_expr;
+ }
+ // Only a key that can actually be NULL needs the disjunct; a NOT NULL
key never widens.
+ // Null-aware joins are single-key; null-equal joins can be multi-key,
so OR every nullable
+ // key. If every key is NOT NULL the filter is left untouched, at full
selectivity.
+ let any_key_is_null = self
+ .on_right
+ .iter()
+ .filter(|key| key.nullable(&self.probe_schema).unwrap_or(true))
Review Comment:
This is a should-never-happen (as you said: keys out of sync with the probe
schema), so I kept `unwrap_or(true)` as the safe degradation: over-widening
only loses a little selectivity, while `false` could drop a NULL the join
needs. Documented it in `9620b97`.
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