Merge pull request ClickHouse#88509 from ClickHouse/backport/25.8/87798

Backport ClickHouse#87798 to 25.8: Fix reading null map subcolumn from Variants that cannot be inside Nullable

Author: rienath

src/DataTypes/DataTypeDynamic.cpp

@@ -215,6 +215,8 @@ std::unique_ptr<IDataType::SubstreamData> DataTypeDynamic::getDynamicSubcolumnDa
     bool is_null_map_subcolumn = subcolumn_nested_name == "null";
     if (is_null_map_subcolumn)
     {
+        if (!subcolumn_type->canBeInsideNullable())
+            return nullptr;
         res->type = std::make_shared<DataTypeUInt8>();
     }
     else if (!subcolumn_nested_name.empty())

src/DataTypes/DataTypeVariant.cpp

@@ -182,7 +182,7 @@ SerializationPtr DataTypeVariant::doGetDefaultSerialization() const
         variant_names.push_back(variant->getName());
     }
 
-    return std::make_shared<SerializationVariant>(std::move(serializations), std::move(variant_names), SerializationVariant::getVariantsDeserializeTextOrder(variants), getName());
+    return std::make_shared<SerializationVariant>(variants, getName());
 }
 
 void DataTypeVariant::forEachChild(const DB::IDataType::ChildCallback & callback) const

src/DataTypes/Serializations/SerializationVariant.cpp

@@ -72,14 +72,7 @@ class SerializationVariant : public ISerialization
 
     using VariantSerializations = std::vector<SerializationPtr>;
 
-    explicit SerializationVariant(
-        const VariantSerializations & variants_,
-        const std::vector<String> & variant_names_,
-        const std::vector<size_t> & deserialize_text_order_,
-        const String & variant_name_)
-        : variants(variants_), variant_names(variant_names_), deserialize_text_order(deserialize_text_order_), variant_name(variant_name_)
-    {
-    }
+    explicit SerializationVariant(const DataTypes & variant_types_, const String & variant_name_);
 
     void enumerateStreams(
         EnumerateStreamsSettings & settings,
@@ -222,8 +215,9 @@ class SerializationVariant : public ISerialization
         std::function<bool(IColumn & variant_columm, const SerializationPtr & nested, ReadBuffer &, const FormatSettings &)> try_deserialize_nested,
         const FormatSettings & settings) const;
 
-    VariantSerializations variants;
+    VariantSerializations variant_serializations;
     std::vector<String> variant_names;
+    DataTypes variant_types;
     std::vector<size_t> deserialize_text_order;
     /// Name of Variant data type for better exception messages.
     String variant_name;