adriangb commented on code in PR #16641:
URL: https://github.com/apache/datafusion/pull/16641#discussion_r2183060691
##########
datafusion/physical-optimizer/src/enforce_sorting/sort_pushdown.rs:
##########
@@ -216,7 +218,42 @@ fn pushdown_sorts_helper(
fn pushdown_requirement_to_children(
plan: &Arc<dyn ExecutionPlan>,
parent_required: OrderingRequirements,
+ parent_fetch: Option<usize>,
) -> Result<Option<Vec<Option<OrderingRequirements>>>> {
+ // If there is a limit on the parent plan we cannot push it down through
operators that change the cardinality.
+ // E.g. consider if LIMIT 2 is applied below a FilteExec that filters out
1/2 of the rows we'll end up with 1 row instead of 2.
+ // If the LIMIT is applied after the FilterExec and the FilterExec returns
> 2 rows we'll end up with 2 rows (correct).
+ if parent_fetch.is_some() {
+ if !plan.supports_limit_pushdown() {
+ return Ok(None);
+ }
Review Comment:
```suggestion
if parent_fetch.is_some() && !plan.supports_limit_pushdown() {
return Ok(None);
```
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