Support Decimal32/64 types (apache#17501)

* Support Decimal32/64 types

* Fix bugs, tests, handle more aggregate functions and schema

* Fill out more parts in expr,common and expr-common

* Some stragglers and overlooked corners

* Actually commit the avg_distinct support

---------

Co-authored-by: Andrew Lamb <[email protected]>

Author: AdamGS

datafusion/common/src/cast.rs

@@ -22,9 +22,10 @@
 
 use crate::{downcast_value, Result};
 use arrow::array::{
-    BinaryViewArray, DurationMicrosecondArray, DurationMillisecondArray,
-    DurationNanosecondArray, DurationSecondArray, Float16Array, Int16Array, Int8Array,
-    LargeBinaryArray, LargeStringArray, StringViewArray, UInt16Array,
+    BinaryViewArray, Decimal32Array, Decimal64Array, DurationMicrosecondArray,
+    DurationMillisecondArray, DurationNanosecondArray, DurationSecondArray, Float16Array,
+    Int16Array, Int8Array, LargeBinaryArray, LargeStringArray, StringViewArray,
+    UInt16Array,
 };
 use arrow::{
     array::{
@@ -97,6 +98,16 @@ pub fn as_uint64_array(array: &dyn Array) -> Result<&UInt64Array> {
     Ok(downcast_value!(array, UInt64Array))
 }
 
+// Downcast Array to Decimal32Array
+pub fn as_decimal32_array(array: &dyn Array) -> Result<&Decimal32Array> {
+    Ok(downcast_value!(array, Decimal32Array))
+}
+
+// Downcast Array to Decimal64Array
+pub fn as_decimal64_array(array: &dyn Array) -> Result<&Decimal64Array> {
+    Ok(downcast_value!(array, Decimal64Array))
+}
+
 // Downcast Array to Decimal128Array
 pub fn as_decimal128_array(array: &dyn Array) -> Result<&Decimal128Array> {
     Ok(downcast_value!(array, Decimal128Array))