fix: downcast to FixedSizeBinaryArray in CASE literal lookup table

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

@@ -3500,6 +3500,52 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_case_when_literal_lookup_fixed_size_binary_to_int32() {
+        let lookup_map = vec![
+            (
+                ScalarValue::FixedSizeBinary(1, Some(vec![1])),
+                ScalarValue::Int32(Some(10)),
+            ),
+            (
+                ScalarValue::FixedSizeBinary(1, Some(vec![2])),
+                ScalarValue::Int32(Some(20)),
+            ),
+        ];
+
+        let input_values = ScalarValue::iter_to_array(vec![
+            ScalarValue::FixedSizeBinary(1, Some(vec![1])),
+            ScalarValue::FixedSizeBinary(1, Some(vec![2])),
+            ScalarValue::FixedSizeBinary(1, Some(vec![3])),
+            ScalarValue::FixedSizeBinary(1, None),
+        ])
+        .expect("valid fixed size binary array");
+
+        let expected_no_else =
+            Arc::new(Int32Array::from(vec![Some(10), Some(20), None, None])) as ArrayRef;
+
+        test_case_when_literal_lookup(
+            Arc::clone(&input_values),
+            &lookup_map,
+            None,
+            expected_no_else,
+        );
+
+        let expected_with_else = Arc::new(Int32Array::from(vec![
+            Some(10),
+            Some(20),
+            Some(99),
+            Some(99),
+        ])) as ArrayRef;
+
+        test_case_when_literal_lookup(
+            input_values,
+            &lookup_map,
+            Some(ScalarValue::Int32(Some(99))),
+            expected_with_else,
+        );
+    }
+
     /// Reproduces https://github.com/apache/datafusion/issues/22173
     ///
     /// Nested self-referential CASE chains (common in rewrite-style projections)

datafusion/physical-expr/src/expressions/case/literal_lookup_table/bytes_like_lookup_table.rs

@@ -106,7 +106,7 @@ fn try_get_bytes_iterator(
 
         DataType::LargeBinary => Box::new(array.as_binary::<i64>().into_iter()),
 
-        DataType::FixedSizeBinary(_) => Box::new(array.as_binary::<i64>().into_iter()),
+        DataType::FixedSizeBinary(_) => Box::new(array.as_fixed_size_binary().iter()),
 
         DataType::Utf8View => Box::new(
             array

datafusion/sqllogictest/test_files/case.slt

@@ -846,6 +846,66 @@ drop table letters;
 statement ok
 drop table letters_binary;
 
+# Regression test for https://github.com/apache/datafusion/issues/26012
+# CASE with two or more FixedSizeBinary WHEN literals
+query I
+SELECT CASE x
+         WHEN arrow_cast(X'01', 'FixedSizeBinary(1)') THEN 1
+         WHEN arrow_cast(X'02', 'FixedSizeBinary(1)') THEN 2
+         ELSE 3
+       END AS r
+FROM (SELECT arrow_cast(X'03', 'FixedSizeBinary(1)') AS x);
+----
+3
+
+query I
+SELECT CASE x
+         WHEN arrow_cast(X'01', 'FixedSizeBinary(1)') THEN 1
+         WHEN arrow_cast(X'02', 'FixedSizeBinary(1)') THEN 2
+         ELSE 3
+       END AS r
+FROM (SELECT arrow_cast(X'02', 'FixedSizeBinary(1)') AS x);
+----
+2
+
+query I
+SELECT CASE x
+         WHEN arrow_cast(X'01', 'FixedSizeBinary(1)') THEN 1
+         WHEN arrow_cast(X'02', 'FixedSizeBinary(1)') THEN 2
+         ELSE 3
+       END AS r
+FROM (SELECT arrow_cast(X'01', 'FixedSizeBinary(1)') AS x);
+----
+1
+
+query I
+SELECT CASE x
+         WHEN arrow_cast(X'01', 'FixedSizeBinary(1)') THEN 1
+         WHEN arrow_cast(X'02', 'FixedSizeBinary(1)') THEN 2
+         ELSE 3
+       END AS r
+FROM (SELECT arrow_cast(NULL, 'FixedSizeBinary(1)') AS x);
+----
+3
+
+query I
+SELECT CASE x
+         WHEN arrow_cast(X'01', 'FixedSizeBinary(1)') THEN 10
+         WHEN arrow_cast(X'02', 'FixedSizeBinary(1)') THEN 20
+         ELSE 99
+       END AS r
+FROM (VALUES
+    (arrow_cast(X'01', 'FixedSizeBinary(1)')),
+    (arrow_cast(X'02', 'FixedSizeBinary(1)')),
+    (arrow_cast(X'03', 'FixedSizeBinary(1)')),
+    (arrow_cast(NULL, 'FixedSizeBinary(1)'))
+) t(x);
+----
+10
+20
+99
+99
+
 # Tests for CASE with boolean expressions
 statement ok
 create table booleans (b boolean) as values (true), (false), (null), (true), (null), (false);