feat[expr-common]: support REE in coalesce (#21919)

We were missing a couple of branches to unwrap REE in
type_union_resolution_coercion.

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- Closes #21918 

## Rationale for this change

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Fix an unexpected error

## What changes are included in this PR?

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PR.
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Type coercion match arms for REE

## Are these changes tested?

Yes, via sql logic tests
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Queries that errored now complete successfully

Signed-off-by: Alfonso Subiotto Marques <alfonso.subiotto@polarsignals.com>

Author: asubiotto

datafusion/expr-common/src/type_coercion/binary.rs

@@ -528,11 +528,12 @@ enum TypeCategory {
 impl From<&DataType> for TypeCategory {
     fn from(data_type: &DataType) -> Self {
         match data_type {
-            // Dict is a special type in arrow, we check the value type
+            // Dict and REE are special types in arrow, we check the value type.
             DataType::Dictionary(_, v) => {
                 let v = v.as_ref();
                 TypeCategory::from(v)
             }
+            DataType::RunEndEncoded(_, v) => TypeCategory::from(v.data_type()),
             _ => {
                 if data_type.is_numeric() {
                     return TypeCategory::Numeric;
@@ -709,6 +710,27 @@ fn type_union_resolution_coercion(
                 None => None,
             }
         }
+        (
+            DataType::RunEndEncoded(lhs_run, lhs_val),
+            DataType::RunEndEncoded(rhs_run, rhs_val),
+        ) => {
+            let new_run =
+                type_union_resolution_coercion(lhs_run.data_type(), rhs_run.data_type())?;
+            let new_val =
+                type_union_resolution_coercion(lhs_val.data_type(), rhs_val.data_type())?;
+            Some(DataType::RunEndEncoded(
+                Arc::new(lhs_run.as_ref().clone().with_data_type(new_run)),
+                Arc::new(lhs_val.as_ref().clone().with_data_type(new_val)),
+            ))
+        }
+        (DataType::RunEndEncoded(run, val), other)
+        | (other, DataType::RunEndEncoded(run, val)) => {
+            let new_val = type_union_resolution_coercion(val.data_type(), other)?;
+            Some(DataType::RunEndEncoded(
+                Arc::clone(run),
+                Arc::new(val.as_ref().clone().with_data_type(new_val)),
+            ))
+        }
         (DataType::Struct(lhs), DataType::Struct(rhs)) => {
             if lhs.len() != rhs.len() {
                 return None;

datafusion/sqllogictest/test_files/coalesce.slt

@@ -443,3 +443,19 @@ query T
 select coalesce(arrow_cast('', 'Utf8View'), arrow_cast('', 'Dictionary(UInt32, Utf8)'));
 ----
 (empty)
+
+# RunEndEncoded column coalesced with a string literal
+statement ok
+create table ree_t as
+select arrow_cast(c, 'RunEndEncoded("run_ends": non-null Int32, "values": Utf8)') as ree_col
+from (values ('hello'), (NULL), ('world')) as t(c);
+
+query ?
+select coalesce(ree_col, '__null__') from ree_t;
+----
+hello
+__null__
+world
+
+statement ok
+drop table ree_t;