Support SQL CTE serializer

[prudnikov]

It would be nice to support CTE serializer, for example

class Contact:
    first_name: str
    last_name: str
    age: int

will produce something like

select "John" as first_name, "Doe" as last_name, 23 as age 
union all
select "Steve" as first_name, "Jobs" as last_name, 56 as age