Make topK return Enum for Enum types

src/AggregateFunctions/AggregateFunctionTopK.cpp

@@ -100,7 +100,8 @@ AggregateFunctionPtr createAggregateFunctionTopK(const std::string & name, const
         threshold = k;
     }
 
-    AggregateFunctionPtr res(createWithNumericType<AggregateFunctionTopK, is_weighted>(*argument_types[0], threshold, load_factor, argument_types, params));
+    AggregateFunctionPtr res(createWithNumericType<AggregateFunctionTopK, is_weighted>(
+        *argument_types[0], threshold, load_factor, argument_types, params));
 
     if (!res)
         res = AggregateFunctionPtr(createWithExtraTypes<is_weighted>(argument_types[0], threshold, load_factor, params));

src/AggregateFunctions/AggregateFunctionTopK.h

@@ -47,7 +47,7 @@ public:
 
     DataTypePtr getReturnType() const override
     {
-        return std::make_shared<DataTypeArray>(std::make_shared<DataTypeNumber<T>>());
+        return std::make_shared<DataTypeArray>(this->argument_types[0]);
     }
 
     void add(AggregateDataPtr place, const IColumn ** columns, size_t row_num, Arena *) const override

tests/queries/0_stateless/01353_topk_enum.reference

@@ -0,0 +1 @@
+['test','world','hello','']

tests/queries/0_stateless/01353_topk_enum.sql

@@ -0,0 +1 @@
+WITH CAST(round(sqrt(number)) % 4 AS Enum('' = 0, 'hello' = 1, 'world' = 2, 'test' = 3)) AS x SELECT topK(10)(x) FROM numbers(1000);