mzabaluev commented on code in PR #19496:
URL: https://github.com/apache/datafusion/pull/19496#discussion_r2668015954
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datafusion/functions-window/src/nth_value.rs:
##########
@@ -370,6 +371,33 @@ impl PartitionEvaluator for NthValueEvaluator {
fn memoize(&mut self, state: &mut WindowAggState) -> Result<()> {
let out = &state.out_col;
let size = out.len();
+ if self.ignore_nulls {
+ match self.state.kind {
+ // Prune on first non-null output in case of FIRST_VALUE
+ NthValueKind::First => {
+ if let Some(nulls) = out.nulls() {
+ if self.state.finalized_result.is_none() {
+ if let Some(valid_index) =
nulls.valid_indices().next() {
+ let result =
+ ScalarValue::try_from_array(out,
valid_index)?;
+ self.state.finalized_result = Some(result);
+ } else {
+ // The output is empty or all nulls, ignore
+ }
+ }
+ if state.window_frame_range.start <
state.window_frame_range.end {
+ state.window_frame_range.start =
+ state.window_frame_range.end - 1;
+ }
Review Comment:
Yes, the intent is to preserve this optimization. In this case, we need one
preceding value for ordering checks in a `RANGE` frame, otherwise the updated
range is not used.
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