jonathanc-n commented on code in PR #20228:
URL: https://github.com/apache/datafusion/pull/20228#discussion_r2783439428
##########
datafusion/physical-plan/src/joins/hash_join/exec.rs:
##########
@@ -1476,12 +1506,53 @@ impl ExecutionPlan for HashJoinExec {
filter: dynamic_filter,
build_accumulator: OnceLock::new(),
}),
+ fetch: self.fetch,
});
result = result.with_updated_node(new_node as Arc<dyn
ExecutionPlan>);
}
}
Ok(result)
}
+
+ fn supports_limit_pushdown(&self) -> bool {
+ // Hash join execution plan does not support pushing limit down
through to children
+ // because the children don't know about the join condition and can't
+ // determine how many rows to produce
+ false
+ }
+
+ fn fetch(&self) -> Option<usize> {
+ self.fetch
+ }
+
+ fn with_fetch(&self, limit: Option<usize>) -> Option<Arc<dyn
ExecutionPlan>> {
+ // Null-aware anti join requires seeing ALL probe rows to check for
NULLs.
+ // If any probe row has NULL, the output must be empty.
+ // We can't stop early or we might miss a NULL and return wrong
results.
+ if self.null_aware {
Review Comment:
If we have two tables like:
table 1 join column: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
table 2 join column: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, NULL]
If we do a LIMIT = 5, when probing, we will match 5 times then the limited
batch coalescer will push the final batch before we hit the NULL.
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