make MinMaxStatistics only care about sorting column statistics

Author: suremarc

datafusion/physical-plan/src/statistics.rs

@@ -73,11 +73,37 @@ impl MinMaxStatistics {
     ) -> Result<Self> {
         use datafusion_common::ScalarValue;
 
-        let statistics = statistics.into_iter().collect::<Vec<_>>();
+        let sort_columns = sort_columns_from_physical_sort_exprs(sort_order).ok_or(
+            DataFusionError::Plan("sort expression must be on column".to_string()),
+        )?;
+
+        let projection = sort_columns.iter().map(|c| c.index()).collect::<Vec<_>>();
+
+        // Project the schema & sort order down to just the relevant columns
+
+        let projected_schema = Arc::new(schema.project(&projection)?);
+
+        let projected_sort_order = LexOrdering {
+            inner: sort_columns
+                .iter()
+                .zip(sort_order.iter())
+                .enumerate()
+                .map(|(i, (col, sort))| PhysicalSortExpr {
+                    expr: Arc::new(Column::new(col.name(), i)),
+                    options: sort.options,
+                })
+                .collect::<Vec<_>>(),
+        };
 
-        // Helper function to get min/max statistics for a given column of projected_schema
+        let projected_statistics = statistics
+            .into_iter()
+            .cloned()
+            .map(|s| s.project(Some(&projection)))
+            .collect::<Vec<_>>();
+
+        // Helper function to get min/max statistics
         let get_min_max = |i: usize| -> Result<(Vec<ScalarValue>, Vec<ScalarValue>)> {
-            Ok(statistics
+            Ok(projected_statistics
                 .iter()
                 .map(|s| {
                     s.column_statistics[i]
@@ -94,31 +120,11 @@ impl MinMaxStatistics {
                 .unzip())
         };
 
-        let sort_columns = sort_columns_from_physical_sort_exprs(sort_order).ok_or(
-            DataFusionError::Plan("sort expression must be on column".to_string()),
-        )?;
-
-        // Project the schema & sort order down to just the relevant columns
-        let min_max_schema = Arc::new(
-            schema
-                .project(&(sort_columns.iter().map(|c| c.index()).collect::<Vec<_>>()))?,
-        );
-        let min_max_sort_order = LexOrdering {
-            inner: sort_columns
-                .iter()
-                .zip(sort_order.iter())
-                .enumerate()
-                .map(|(i, (col, sort))| PhysicalSortExpr {
-                    expr: Arc::new(Column::new(col.name(), i)),
-                    options: sort.options,
-                })
-                .collect::<Vec<_>>(),
-        };
-
         let (min_values, max_values): (Vec<_>, Vec<_>) = sort_columns
             .iter()
-            .map(|c| {
-                let (min, max) = get_min_max(c.index()).map_err(|e| {
+            .enumerate()
+            .map(|(i, c)| {
+                let (min, max) = get_min_max(i).map_err(|e| {
                     e.context(format!("get min/max for column: '{}'", c.name()))
                 })?;
                 Ok((
@@ -132,14 +138,14 @@ impl MinMaxStatistics {
             .unzip();
 
         Self::new(
-            &min_max_sort_order,
-            &min_max_schema,
-            RecordBatch::try_new(Arc::clone(&min_max_schema), min_values).map_err(
+            &projected_sort_order,
+            &projected_schema,
+            RecordBatch::try_new(Arc::clone(&projected_schema), min_values).map_err(
                 |e| {
                     DataFusionError::ArrowError(e, Some("\ncreate min batch".to_string()))
                 },
             )?,
-            RecordBatch::try_new(Arc::clone(&min_max_schema), max_values).map_err(
+            RecordBatch::try_new(Arc::clone(&projected_schema), max_values).map_err(
                 |e| {
                     DataFusionError::ArrowError(e, Some("\ncreate max batch".to_string()))
                 },