martin-g commented on code in PR #25672:
URL: https://github.com/apache/datafusion/pull/25672#discussion_r4091787497
##########
datafusion/optimizer/src/push_down_limit.rs:
##########
@@ -171,8 +171,16 @@ fn rewrite_limit(mut limit: Limit) ->
Result<Transformed<LogicalPlan>> {
}
} else {
sort.fetch = new_fetch;
- limit.input = Arc::new(LogicalPlan::Sort(sort));
- Ok(Transformed::yes(LogicalPlan::Limit(limit)))
+ if skip > 0 {
+ limit.input = Arc::new(LogicalPlan::Sort(sort));
+ Ok(Transformed::yes(LogicalPlan::Limit(limit)))
+ } else {
+ // With `skip = 0` the Sort's fetch already caps the
output,
+ // so drop the Limit now instead of on the next pass. The
+ // Sort then replaces the Limit as the visited node and its
+ // own visit is skipped, so apply the TopK pushdown here.
+ Ok(Transformed::yes(push_topk_through_join(sort)?.data))
Review Comment:
```suggestion
push_topk_through_join(sort)
```
?
`push_topk_through_join()` may return `Transformed::no()`
##########
datafusion/optimizer/src/push_down_limit.rs:
##########
Review Comment:
Would that benefit of using `push_topk_through_join(sort)` too ?!
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