The only way to use this feature is to specify an empty database name in Distributed table definition, but then you get a warning:

```
CREATE TABLE `demo_loan_all` (...) ENGINE=Distributed(test_cluster_two_shards_different_databases, '', demo_loan_01568, cityHash64(id));

<Warning> StorageDistributed (demo_loan_all): Name of remote database is empty. Default database will be used implicitly.
```
{
    const Settings & settings = local_context->getSettingsRef();
    std::shared_ptr<StorageDistributed> storage_src;
    auto & select = query.select->as<ASTSelectWithUnionQuery &>();
    auto new_query = std::dynamic_pointer_cast<ASTInsertQuery>(query.clone());
    if (select.list_of_selects->children.size() == 1)
    {
        if (auto * select_query = select.list_of_selects->children.at(0)->as<ASTSelectQuery>())
        {
            JoinedTables joined_tables(Context::createCopy(local_context), *select_query);
            if (joined_tables.tablesCount() == 1)
            {
                storage_src = std::dynamic_pointer_cast<StorageDistributed>(joined_tables.getLeftTableStorage());
                if (storage_src)
                {
                    const auto select_with_union_query = std::make_shared<ASTSelectWithUnionQuery>();
                    select_with_union_query->list_of_selects = std::make_shared<ASTExpressionList>();
                    auto new_select_query = std::dynamic_pointer_cast<ASTSelectQuery>(select_query->clone());
                    select_with_union_query->list_of_selects->children.push_back(new_select_query);
                    new_select_query->replaceDatabaseAndTable(storage_src->getRemoteDatabaseName(), storage_src->getRemoteTableName());
                    new_query->select = select_with_union_query;
                }
            }
        }
    }
    if (!storage_src || storage_src->getClusterName() != getClusterName())
    {
        return nullptr;
    }
    if (settings.parallel_distributed_insert_select == PARALLEL_DISTRIBUTED_INSERT_SELECT_ALL)