feat: support nested key for get_field (apache#18394)

## Which issue does this PR close?

## Rationale for this change

get_field doesn't support nested key

## What changes are included in this PR?

support nested key

## Are these changes tested?

UT

## Are there any user-facing changes?

No

---------

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

Author: 2 people

datafusion/functions/src/core/getfield.rs

@@ -245,6 +245,46 @@ impl ScalarUDFImpl for GetFieldFunc {
             Ok(ColumnarValue::Array(data))
         }
 
+        fn process_map_with_nested_key(
+            array: Arc<dyn Array>,
+            key_array: Arc<dyn Array>,
+        ) -> Result<ColumnarValue> {
+            let map_array = as_map_array(array.as_ref())?;
+
+            let comparator = make_comparator(
+                map_array.keys().as_ref(),
+                key_array.as_ref(),
+                SortOptions::default(),
+            )?;
+
+            let original_data = map_array.entries().column(1).to_data();
+            let capacity = Capacities::Array(original_data.len());
+            let mut mutable =
+                MutableArrayData::with_capacities(vec![&original_data], true, capacity);
+
+            for entry in 0..map_array.len() {
+                let start = map_array.value_offsets()[entry] as usize;
+                let end = map_array.value_offsets()[entry + 1] as usize;
+
+                let mut found_match = false;
+                for i in start..end {
+                    if comparator(i, 0).is_eq() {
+                        mutable.extend(0, i, i + 1);
+                        found_match = true;
+                        break;
+                    }
+                }
+
+                if !found_match {
+                    mutable.extend_nulls(1);
+                }
+            }
+
+            let data = mutable.freeze();
+            let data = make_array(data);
+            Ok(ColumnarValue::Array(data))
+        }
+
         match (array.data_type(), name) {
             (DataType::Map(_, _), ScalarValue::List(arr)) => {
                 let key_array: Arc<dyn Array> = arr;
@@ -256,7 +296,7 @@ impl ScalarUDFImpl for GetFieldFunc {
             (DataType::Map(_, _), other) => {
                 let data_type = other.data_type();
                 if data_type.is_nested() {
-                    exec_err!("unsupported type {} for map access", data_type)
+                    process_map_with_nested_key(array, other.to_array()?)
                 } else {
                     process_map_array(array, other.to_array()?)
                 }

datafusion/sqllogictest/test_files/map.slt

@@ -544,11 +544,19 @@ SELECT (CASE WHEN 1 > 0 THEN MAP {'x': 100} ELSE MAP {'y': 200} END)['x'];
 ----
 100
 
-# TODO(https://github.com/apache/datafusion/issues/11785): fix accessing map with non-string key
-# query ?
-# SELECT MAP { MAP {1:'a', 2:'b'}:1, MAP {1:'c', 2:'d'}:2 }[MAP {1:'a', 2:'b'}];
-# ----
-# 1
+# fix accessing map with nested key
+query I
+SELECT MAP { MAP {1:'a', 2:'b'}:1, MAP {1:'c', 2:'d'}:2 }[MAP {1:'a', 2:'b'}];
+----
+1
+
+query I
+SELECT MAP { MAP {1:'a', 2:'b'}:1, MAP {1:'c', 2:'d'}:2 }[MAP {2:'b', 1:'a'}];
+----
+NULL
+
+# TODO(https://github.com/apache/datafusion/pull/18394): Test accessing map with empty map as key
+# TODO(https://github.com/apache/datafusion/pull/18394): Test accessing map with null map as key
 
 # accessing map with non-string key
 query I