optimize nth_value

datafusion/src/physical_plan/expressions/mod.rs

@@ -59,7 +59,7 @@ pub use literal::{lit, Literal};
 pub use min_max::{Max, Min};
 pub use negative::{negative, NegativeExpr};
 pub use not::{not, NotExpr};
-pub use nth_value::{FirstValue, LastValue, NthValue};
+pub use nth_value::NthValue;
 pub use nullif::{nullif_func, SUPPORTED_NULLIF_TYPES};
 pub use row_number::RowNumber;
 pub use sum::{sum_return_type, Sum};

datafusion/src/physical_plan/expressions/nth_value.rs

@@ -27,128 +27,69 @@ use std::any::Any;
 use std::convert::TryFrom;
 use std::sync::Arc;
 
-/// first_value expression
+/// nth_value kind
+#[derive(Debug, Copy, Clone)]
+enum NthValueKind {
+    First,
+    Last,
+    Nth(u32),
+}
+
+/// nth_value expression
 #[derive(Debug)]
-pub struct FirstValue {
+pub struct NthValue {
     name: String,
-    data_type: DataType,
     expr: Arc<dyn PhysicalExpr>,
+    data_type: DataType,
+    kind: NthValueKind,
 }
 
-impl FirstValue {
+impl NthValue {
     /// Create a new FIRST_VALUE window aggregate function
-    pub fn new(expr: Arc<dyn PhysicalExpr>, name: String, data_type: DataType) -> Self {
+    pub fn first_value(
+        name: String,
+        expr: Arc<dyn PhysicalExpr>,
+        data_type: DataType,
+    ) -> Self {
         Self {
             name,
-            data_type,
             expr,
+            data_type,
+            kind: NthValueKind::First,
         }
     }
-}
-
-impl BuiltInWindowFunctionExpr for FirstValue {
-    /// Return a reference to Any that can be used for downcasting
-    fn as_any(&self) -> &dyn Any {
-        self
-    }
-
-    fn field(&self) -> Result<Field> {
-        let nullable = true;
-        Ok(Field::new(&self.name, self.data_type.clone(), nullable))
-    }
-
-    fn expressions(&self) -> Vec<Arc<dyn PhysicalExpr>> {
-        vec![self.expr.clone()]
-    }
 
-    fn name(&self) -> &str {
-        &self.name
-    }
-
-    fn create_accumulator(&self) -> Result<Box<dyn WindowAccumulator>> {
-        Ok(Box::new(NthValueAccumulator::try_new(
-            1,
-            self.data_type.clone(),
-        )?))
-    }
-}
-
-// sql values start with 1, so we can use 0 to indicate the special last value behavior
-const SPECIAL_SIZE_VALUE_FOR_LAST: u32 = 0;
-
-/// last_value expression
-#[derive(Debug)]
-pub struct LastValue {
-    name: String,
-    data_type: DataType,
-    expr: Arc<dyn PhysicalExpr>,
-}
-
-impl LastValue {
-    /// Create a new FIRST_VALUE window aggregate function
-    pub fn new(expr: Arc<dyn PhysicalExpr>, name: String, data_type: DataType) -> Self {
+    /// Create a new LAST_VALUE window aggregate function
+    pub fn last_value(
+        name: String,
+        expr: Arc<dyn PhysicalExpr>,
+        data_type: DataType,
+    ) -> Self {
         Self {
             name,
-            data_type,
             expr,
+            data_type,
+            kind: NthValueKind::Last,
         }
     }
-}
 
-impl BuiltInWindowFunctionExpr for LastValue {
-    /// Return a reference to Any that can be used for downcasting
-    fn as_any(&self) -> &dyn Any {
-        self
-    }
-
-    fn field(&self) -> Result<Field> {
-        let nullable = true;
-        Ok(Field::new(&self.name, self.data_type.clone(), nullable))
-    }
-
-    fn expressions(&self) -> Vec<Arc<dyn PhysicalExpr>> {
-        vec![self.expr.clone()]
-    }
-
-    fn name(&self) -> &str {
-        &self.name
-    }
-
-    fn create_accumulator(&self) -> Result<Box<dyn WindowAccumulator>> {
-        Ok(Box::new(NthValueAccumulator::try_new(
-            SPECIAL_SIZE_VALUE_FOR_LAST,
-            self.data_type.clone(),
-        )?))
-    }
-}
-
-/// nth_value expression
-#[derive(Debug)]
-pub struct NthValue {
-    name: String,
-    n: u32,
-    data_type: DataType,
-    expr: Arc<dyn PhysicalExpr>,
-}
-
-impl NthValue {
     /// Create a new NTH_VALUE window aggregate function
-    pub fn try_new(
-        expr: Arc<dyn PhysicalExpr>,
+    pub fn nth_value(
         name: String,
-        n: u32,
+        expr: Arc<dyn PhysicalExpr>,
         data_type: DataType,
+        n: u32,
     ) -> Result<Self> {
-        if n == SPECIAL_SIZE_VALUE_FOR_LAST {
+        if n == 0 {
             Err(DataFusionError::Execution(
                 "nth_value expect n to be > 0".to_owned(),
             ))
         } else {
             Ok(Self {
                 name,
-                n,
-                data_type,
                 expr,
+                data_type,
+                kind: NthValueKind::Nth(n),
             })
         }
     }
@@ -175,27 +116,24 @@ impl BuiltInWindowFunctionExpr for NthValue {
 
     fn create_accumulator(&self) -> Result<Box<dyn WindowAccumulator>> {
         Ok(Box::new(NthValueAccumulator::try_new(
-            self.n,
+            self.kind,
             self.data_type.clone(),
         )?))
     }
 }
 
 #[derive(Debug)]
 struct NthValueAccumulator {
-    // n the target nth_value, however we'll reuse it for last_value acc, so when n == 0 it specifically
-    // means last; also note that it is totally valid for n to be larger than the number of rows input
-    // in which case all the values shall be null
-    n: u32,
+    kind: NthValueKind,
     offset: u32,
     value: ScalarValue,
 }
 
 impl NthValueAccumulator {
     /// new count accumulator
-    pub fn try_new(n: u32, data_type: DataType) -> Result<Self> {
+    pub fn try_new(kind: NthValueKind, data_type: DataType) -> Result<Self> {
         Ok(Self {
-            n,
+            kind,
             offset: 0,
             // null value of that data_type by default
             value: ScalarValue::try_from(&data_type)?,
@@ -205,19 +143,98 @@ impl NthValueAccumulator {
 
 impl WindowAccumulator for NthValueAccumulator {
     fn scan(&mut self, values: &[ScalarValue]) -> Result<Option<ScalarValue>> {
-        if self.n == SPECIAL_SIZE_VALUE_FOR_LAST {
-            // for last_value function
-            self.value = values[0].clone();
-        } else if self.offset < self.n {
-            self.offset += 1;
-            if self.offset == self.n {
+        self.offset += 1;
+        match self.kind {
+            NthValueKind::Last => {
+                self.value = values[0].clone();
+            }
+            NthValueKind::First if self.offset == 1 => {
                 self.value = values[0].clone();
             }
+            NthValueKind::Nth(n) if self.offset == n => {
+                self.value = values[0].clone();
+            }
+            _ => {}
         }
+
         Ok(None)
     }
 
     fn evaluate(&self) -> Result<Option<ScalarValue>> {
         Ok(Some(self.value.clone()))
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::error::Result;
+    use crate::physical_plan::expressions::col;
+    use arrow::record_batch::RecordBatch;
+    use arrow::{array::*, datatypes::*};
+
+    fn test_i32_result(expr: Arc<NthValue>, expected: i32) -> Result<()> {
+        let arr: ArrayRef = Arc::new(Int32Array::from(vec![1, -2, 3, -4, 5, -6, 7, 8]));
+        let schema = Schema::new(vec![Field::new("arr", DataType::Int32, false)]);
+        let batch = RecordBatch::try_new(Arc::new(schema), vec![arr])?;
+
+        let mut acc = expr.create_accumulator()?;
+        let expr = expr.expressions();
+        let values = expr
+            .iter()
+            .map(|e| e.evaluate(&batch))
+            .map(|r| r.map(|v| v.into_array(batch.num_rows())))
+            .collect::<Result<Vec<_>>>()?;
+        let result = acc.scan_batch(batch.num_rows(), &values)?;
+        assert_eq!(false, result.is_some());
+        let result = acc.evaluate()?;
+        assert_eq!(Some(ScalarValue::Int32(Some(expected))), result);
+        Ok(())
+    }
+
+    #[test]
+    fn first_value() -> Result<()> {
+        let first_value = Arc::new(NthValue::first_value(
+            "first_value".to_owned(),
+            col("arr"),
+            DataType::Int32,
+        ));
+        test_i32_result(first_value, 1)?;
+        Ok(())
+    }
+
+    #[test]
+    fn last_value() -> Result<()> {
+        let last_value = Arc::new(NthValue::last_value(
+            "last_value".to_owned(),
+            col("arr"),
+            DataType::Int32,
+        ));
+        test_i32_result(last_value, 8)?;
+        Ok(())
+    }
+
+    #[test]
+    fn nth_value_1() -> Result<()> {
+        let nth_value = Arc::new(NthValue::nth_value(
+            "nth_value".to_owned(),
+            col("arr"),
+            DataType::Int32,
+            1,
+        )?);
+        test_i32_result(nth_value, 1)?;
+        Ok(())
+    }
+
+    #[test]
+    fn nth_value_2() -> Result<()> {
+        let nth_value = Arc::new(NthValue::nth_value(
+            "nth_value".to_owned(),
+            col("arr"),
+            DataType::Int32,
+            1,
+        )?);
+        test_i32_result(nth_value, -2)?;
+        Ok(())
+    }
+}

datafusion/src/physical_plan/windows.rs

@@ -20,7 +20,7 @@
 use crate::error::{DataFusionError, Result};
 use crate::physical_plan::{
     aggregates,
-    expressions::{FirstValue, LastValue, Literal, NthValue, RowNumber},
+    expressions::{Literal, NthValue, RowNumber},
     type_coercion::coerce,
     window_functions::signature_for_built_in,
     window_functions::BuiltInWindowFunctionExpr,
@@ -105,19 +105,19 @@ fn create_built_in_window_expr(
                 .map_err(|e| DataFusionError::Execution(format!("{:?}", e)))?;
             let n: u32 = n as u32;
             let data_type = args[0].data_type(input_schema)?;
-            Ok(Arc::new(NthValue::try_new(arg, name, n, data_type)?))
+            Ok(Arc::new(NthValue::nth_value(name, arg, data_type, n)?))
         }
         BuiltInWindowFunction::FirstValue => {
             let arg =
                 coerce(args, input_schema, &signature_for_built_in(fun))?[0].clone();
             let data_type = args[0].data_type(input_schema)?;
-            Ok(Arc::new(FirstValue::new(arg, name, data_type)))
+            Ok(Arc::new(NthValue::first_value(name, arg, data_type)))
         }
         BuiltInWindowFunction::LastValue => {
             let arg =
                 coerce(args, input_schema, &signature_for_built_in(fun))?[0].clone();
             let data_type = args[0].data_type(input_schema)?;
-            Ok(Arc::new(LastValue::new(arg, name, data_type)))
+            Ok(Arc::new(NthValue::last_value(name, arg, data_type)))
         }
         _ => Err(DataFusionError::NotImplemented(format!(
             "Window function with {:?} not yet implemented",