suibianwanwank commented on code in PR #15697:
URL: https://github.com/apache/datafusion/pull/15697#discussion_r2042485745
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datafusion/physical-plan/src/topk/mod.rs:
##########
@@ -202,27 +204,121 @@ impl TopK {
})
.collect::<Result<Vec<_>>>()?;
+ // Selected indices in the input batch.
+ // Some indices may be pre-filtered if they exceed the heap’s current
max value.
+
+ let mut selected_rows = None;
+
+ // If the heap doesn't have k elements yet, we can't create thresholds
+ if let Some(max_row) = self.heap.max() {
+ // Get the batch that contains the max row
+ let batch_entry = match self.heap.store.get(max_row.batch_id) {
+ Some(entry) => entry,
+ None => return internal_err!("Invalid batch ID in TopKRow"),
+ };
+
+ // Extract threshold values for each sort expression
+ // TODO: create a filter for each key that respects lexical
ordering
+ // in the form of col0 < threshold0 || col0 == threshold0 && (col1
< threshold1 || ...)
+ // This could use BinaryExpr to benefit from short circuiting and
early evaluation
+ // https://github.com/apache/datafusion/issues/15698
+ // Extract the value for this column from the max row
+ let expr = Arc::clone(&self.expr[0].expr);
+ let value = expr.evaluate(&batch_entry.batch.slice(max_row.index,
1))?;
+
+ // Convert to scalar value - should be a single value since we're
evaluating on a single row batch
+ let threshold = Scalar::new(value.to_array(1)?);
Review Comment:
Do we need to skip the case of being NULL here, because `NULL > any number`
is false.
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