Re: Virtual generated columns

On Tue, Feb 18, 2025 at 7:09 PM Richard Guo <guofenglinux(at)gmail(dot)com> wrote:
> It seems to me that, for a relation in the rangetable that has virtual
> generated columns, we can consider it a subquery to some extent. For
> instance, suppose we have a query:
>
> select ... from ... join t on ...;
>
> and suppose t.b is a virtual generated column. We can consider this
> query as:
>
> select ... from ... join (select a, expr() as b from t) as t on ...;
>
> In this sense, I'm wondering if we can leverage the
> pullup_replace_vars architecture to expand the virtual generated
> columns. I believe this would help avoid a lot of duplicate code with
> pullup_replace_vars_callback.

I had a try with this idea, and attached is what I came up with. It
fixes all the mentioned issues but still requires significant
refinement, particularly due to the lack of comments. By leveraging
the pullup_replace_vars architecture to expand the virtual generated
columns, it saves a lot of duplicate code.

Thanks
Richard