houqp commented on a change in pull request #7253:
URL: https://github.com/apache/arrow/pull/7253#discussion_r429569531



##########
File path: rust/datafusion/src/optimizer/utils.rs
##########
@@ -131,116 +131,90 @@ pub fn exprlist_to_fields(expr: &[Expr], input_schema: 
&Schema) -> Result<Vec<Fi
 
 /// Given two datatypes, determine the supertype that both types can safely be 
cast to
 pub fn get_supertype(l: &DataType, r: &DataType) -> Result<DataType> {
-    match _get_supertype(l, r) {
-        Some(dt) => Ok(dt),
-        None => _get_supertype(r, l).ok_or_else(|| {
-            ExecutionError::InternalError(format!(
-                "Failed to determine supertype of {:?} and {:?}",
-                l, r
-            ))
-        }),
-    }
-}
-
-/// Given two datatypes, determine the supertype that both types can safely be 
cast to
-fn _get_supertype(l: &DataType, r: &DataType) -> Option<DataType> {
     use arrow::datatypes::DataType::*;
-    match (l, r) {
-        (UInt8, Int8) => Some(Int8),
-        (UInt8, Int16) => Some(Int16),
-        (UInt8, Int32) => Some(Int32),
-        (UInt8, Int64) => Some(Int64),
-
-        (UInt16, Int16) => Some(Int16),
-        (UInt16, Int32) => Some(Int32),
-        (UInt16, Int64) => Some(Int64),
-
-        (UInt32, Int32) => Some(Int32),
-        (UInt32, Int64) => Some(Int64),
-
-        (UInt64, Int64) => Some(Int64),
-
-        (Int8, UInt8) => Some(Int8),
-
-        (Int16, UInt8) => Some(Int16),
-        (Int16, UInt16) => Some(Int16),
-
-        (Int32, UInt8) => Some(Int32),
-        (Int32, UInt16) => Some(Int32),
-        (Int32, UInt32) => Some(Int32),
-
-        (Int64, UInt8) => Some(Int64),
-        (Int64, UInt16) => Some(Int64),
-        (Int64, UInt32) => Some(Int64),
-        (Int64, UInt64) => Some(Int64),
-
-        (UInt8, UInt8) => Some(UInt8),
-        (UInt8, UInt16) => Some(UInt16),
-        (UInt8, UInt32) => Some(UInt32),
-        (UInt8, UInt64) => Some(UInt64),
-        (UInt8, Float32) => Some(Float32),
-        (UInt8, Float64) => Some(Float64),
 
-        (UInt16, UInt8) => Some(UInt16),
-        (UInt16, UInt16) => Some(UInt16),
-        (UInt16, UInt32) => Some(UInt32),
-        (UInt16, UInt64) => Some(UInt64),
-        (UInt16, Float32) => Some(Float32),
-        (UInt16, Float64) => Some(Float64),
-
-        (UInt32, UInt8) => Some(UInt32),
-        (UInt32, UInt16) => Some(UInt32),
-        (UInt32, UInt32) => Some(UInt32),
-        (UInt32, UInt64) => Some(UInt64),
-        (UInt32, Float32) => Some(Float32),
-        (UInt32, Float64) => Some(Float64),
-
-        (UInt64, UInt8) => Some(UInt64),
-        (UInt64, UInt16) => Some(UInt64),
-        (UInt64, UInt32) => Some(UInt64),
-        (UInt64, UInt64) => Some(UInt64),
-        (UInt64, Float32) => Some(Float32),
-        (UInt64, Float64) => Some(Float64),
-
-        (Int8, Int8) => Some(Int8),
-        (Int8, Int16) => Some(Int16),
-        (Int8, Int32) => Some(Int32),
-        (Int8, Int64) => Some(Int64),
-        (Int8, Float32) => Some(Float32),
-        (Int8, Float64) => Some(Float64),
-
-        (Int16, Int8) => Some(Int16),
-        (Int16, Int16) => Some(Int16),
-        (Int16, Int32) => Some(Int32),
-        (Int16, Int64) => Some(Int64),
-        (Int16, Float32) => Some(Float32),
-        (Int16, Float64) => Some(Float64),
-
-        (Int32, Int8) => Some(Int32),
-        (Int32, Int16) => Some(Int32),
-        (Int32, Int32) => Some(Int32),
-        (Int32, Int64) => Some(Int64),
-        (Int32, Float32) => Some(Float32),
-        (Int32, Float64) => Some(Float64),
-
-        (Int64, Int8) => Some(Int64),
-        (Int64, Int16) => Some(Int64),
-        (Int64, Int32) => Some(Int64),
-        (Int64, Int64) => Some(Int64),
-        (Int64, Float32) => Some(Float32),
-        (Int64, Float64) => Some(Float64),
-
-        (Float32, Float32) => Some(Float32),
-        (Float32, Float64) => Some(Float64),
-        (Float64, Float32) => Some(Float64),
-        (Float64, Float64) => Some(Float64),
-
-        (Utf8, _) => Some(Utf8),
-        (_, Utf8) => Some(Utf8),
-
-        (Boolean, Boolean) => Some(Boolean),
+    if l == r {
+        return Ok(l.clone());
+    }
 
+    let super_type = match l {
+        UInt8 => match r {
+            UInt16 | UInt32 | UInt64 => Some(r.clone()),
+            Int16 | Int32 | Int64 => Some(r.clone()),
+            Float32 | Float64 => Some(r.clone()),
+            _ => None,
+        },
+        UInt16 => match r {
+            UInt8 => Some(l.clone()),
+            UInt32 | UInt64 => Some(r.clone()),
+            Int8 => Some(l.clone()),
+            Int32 | Int64 => Some(r.clone()),
+            Float32 | Float64 => Some(r.clone()),
+            _ => None,
+        },
+        UInt32 => match r {
+            UInt8 | UInt16 => Some(l.clone()),
+            UInt64 => Some(r.clone()),
+            Int8 | Int16 => Some(l.clone()),
+            Int64 => Some(r.clone()),
+            Float32 | Float64 => Some(r.clone()),
+            _ => None,
+        },
+        UInt64 => match r {
+            UInt8 | UInt16 | UInt32 => Some(l.clone()),
+            Int8 | Int16 | Int32 => Some(l.clone()),
+            Float32 | Float64 => Some(r.clone()),
+            _ => None,
+        },
+        Int8 => match r {

Review comment:
       should we support signed and unsigned with the same width as well? for 
example (int8, uint8) -> int16.




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