Backport #48999 to 23.3: Fix aggregate empty string error

src/Interpreters/Aggregator.h

@@ -301,11 +301,13 @@ struct AggregationMethodStringNoCache
     {
         if constexpr (nullable)
         {
-            static_cast<ColumnNullable *>(key_columns[0])->insertData(key.data, key.size);
+            ColumnNullable & column_nullable = assert_cast<ColumnNullable &>(*key_columns[0]);
+            assert_cast<ColumnString &>(column_nullable.getNestedColumn()).insertData(key.data, key.size);
+            column_nullable.getNullMapData().push_back(0);
         }
         else
         {
-            static_cast<ColumnString *>(key_columns[0])->insertData(key.data, key.size);
+            assert_cast<ColumnString &>(*key_columns[0]).insertData(key.data, key.size);
         }
     }
 };
@@ -339,7 +341,7 @@ struct AggregationMethodFixedString
 
     static void insertKeyIntoColumns(StringRef key, std::vector<IColumn *> & key_columns, const Sizes &)
     {
-        static_cast<ColumnFixedString *>(key_columns[0])->insertData(key.data, key.size);
+        assert_cast<ColumnFixedString &>(*key_columns[0]).insertData(key.data, key.size);
     }
 };
 
@@ -373,11 +375,11 @@ struct AggregationMethodFixedStringNoCache
     {
         if constexpr (nullable)
         {
-            static_cast<ColumnNullable *>(key_columns[0])->insertData(key.data, key.size);
+            assert_cast<ColumnNullable &>(*key_columns[0]).insertData(key.data, key.size);
         }
         else
         {
-            static_cast<ColumnFixedString *>(key_columns[0])->insertData(key.data, key.size);
+            assert_cast<ColumnFixedString &>(*key_columns[0]).insertData(key.data, key.size);
         }
     }
 };

tests/queries/0_stateless/02719_aggregate_with_empty_string_key.reference

@@ -0,0 +1,4 @@
+-----------String------------
+\N	1
+	2
+s	1

tests/queries/0_stateless/02719_aggregate_with_empty_string_key.sql

@@ -0,0 +1,7 @@
+drop table if exists test ;
+create table test(str Nullable(String), i Int64) engine=Memory();
+insert into test values(null, 1),('', 2),('s', 1);
+select '-----------String------------';
+select str ,max(i) from test group by str;
+
+drop table test;