fix: flat KNN column stats order doesn't match schema (#3451)

this causes an error when query with distance range, and there are
unindexed rows

---------

Signed-off-by: BubbleCal <bubble-cal@outlook.com>

Author: BubbleCal

rust/lance/src/io/exec/knn.rs

@@ -11,6 +11,7 @@ use arrow_array::{
     ArrayRef, RecordBatch, StringArray,
 };
 use arrow_schema::{DataType, Field, Schema, SchemaRef};
+use datafusion::common::ColumnStatistics;
 use datafusion::error::{DataFusionError, Result as DataFusionResult};
 use datafusion::physical_plan::PlanProperties;
 use datafusion::physical_plan::{
@@ -184,18 +185,30 @@ impl ExecutionPlan for KNNVectorDistanceExec {
 
     fn statistics(&self) -> DataFusionResult<Statistics> {
         let inner_stats = self.input.statistics()?;
-        let dist_col_stats = inner_stats.column_statistics[0].clone();
+        let schema = self.input.schema();
+        let dist_stats = inner_stats
+            .column_statistics
+            .iter()
+            .zip(schema.fields())
+            .find(|(_, field)| field.name() == &self.column)
+            .map(|(stats, _)| ColumnStatistics {
+                null_count: stats.null_count,
+                ..Default::default()
+            })
+            .unwrap_or_default();
         let column_statistics = inner_stats
             .column_statistics
             .into_iter()
-            .chain([dist_col_stats])
+            .zip(schema.fields())
+            .filter(|(_, field)| field.name() != DIST_COL)
+            .map(|(stats, _)| stats)
+            .chain(std::iter::once(dist_stats))
             .collect::<Vec<_>>();
         Ok(Statistics {
             num_rows: inner_stats.num_rows,
             column_statistics,
             ..Statistics::new_unknown(self.schema().as_ref())
         })
-        // self.input.statistics()
     }
 
     fn properties(&self) -> &PlanProperties {