revise some scalarValue fn implementation

Author: WinkerDu

datafusion/common/src/scalar.rs

@@ -39,7 +39,7 @@ use std::{convert::TryFrom, fmt, iter::repeat, sync::Arc};
 /// This is the single-valued counter-part of arrow’s `Array`.
 #[derive(Clone)]
 pub enum ScalarValue {
-    /// represents null
+    /// represents `DataType::Null` (castable to/from any other type)
     Null,
     /// true or false value
     Boolean(Option<bool>),
@@ -172,6 +172,7 @@ impl PartialEq for ScalarValue {
             (IntervalMonthDayNano(_), _) => false,
             (Struct(v1, t1), Struct(v2, t2)) => v1.eq(v2) && t1.eq(t2),
             (Struct(_, _), _) => false,
+            (Null, Null) => true,
             (Null, _) => false,
         }
     }
@@ -273,6 +274,7 @@ impl PartialOrd for ScalarValue {
                 }
             }
             (Struct(_, _), _) => None,
+            (Null, Null) => Some(Ordering::Equal),
             (Null, _) => None,
         }
     }
@@ -844,10 +846,7 @@ impl ScalarValue {
                     ScalarValue::iter_to_decimal_array(scalars, precision, scale)?;
                 Arc::new(decimal_array)
             }
-            DataType::Null => {
-                let null_array = ScalarValue::iter_to_null_array(scalars)?;
-                Arc::new(null_array)
-            }
+            DataType::Null => ScalarValue::iter_to_null_array(scalars),
             DataType::Boolean => build_array_primitive!(BooleanArray, Boolean),
             DataType::Float32 => build_array_primitive!(Float32Array, Float32),
             DataType::Float64 => build_array_primitive!(Float64Array, Float64),
@@ -980,18 +979,15 @@ impl ScalarValue {
         Ok(array)
     }
 
-    fn iter_to_null_array(
-        scalars: impl IntoIterator<Item = ScalarValue>,
-    ) -> Result<NullArray> {
+    fn iter_to_null_array(scalars: impl IntoIterator<Item = ScalarValue>) -> ArrayRef {
         let length =
             scalars
                 .into_iter()
                 .fold(0usize, |r, element: ScalarValue| match element {
                     ScalarValue::Null => r + 1,
                     _ => unreachable!(),
                 });
-        let array = NullArray::new(length);
-        Ok(array)
+        new_null_array(&DataType::Null, length)
     }
 
     fn iter_to_decimal_array(
@@ -1550,7 +1546,7 @@ impl ScalarValue {
                 eq_array_primitive!(array, index, IntervalMonthDayNanoArray, val)
             }
             ScalarValue::Struct(_, _) => unimplemented!(),
-            ScalarValue::Null => false,
+            ScalarValue::Null => array.data().is_null(index),
         }
     }
 

datafusion/physical-expr/src/expressions/binary.rs

@@ -1278,7 +1278,7 @@ impl BinaryExpr {
             Operator::NotEq => neq_dyn(&left, &right),
             Operator::IsDistinctFrom => {
                 match (left_data_type, right_data_type) {
-                    // exchange lhs and rhs to when lhs is Null since `binary_array_op` is
+                    // exchange lhs and rhs when lhs is Null, since `binary_array_op` is
                     // always try to down cast array according to $LEFT expression.
                     (DataType::Null, _) => {
                         binary_array_op!(right, left, is_distinct_from)