Re: Remove restrictions in recursive query

On Thu, Mar 27, 2025 at 5:38 PM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> It's not a problem if UNION ALL is used within the initial_query and
> it's not a problem if UNION ALL is used within the iterated_query. But
> you can't apply ORDER BY to the result of the UNION, because the UNION
> is kind of fake -- we're not running the UNION as a single query,
> we're running the two halves separately, the first once and the second
> as many times as needed.

I understand that we can only apply ORDER BY separately in the
initial/iterated query. What disturbs me here is that the UNION
operator has associativity precedence over the ORDER BY only when
inside a recursive CTE. Consider the following query:

SELECT 1 UNION SELECT 1 GROUP BY 1;

It returns 2 rows. The GROUP BY clause attaches to the second
selectStmt without the need to add parenthesis. I would expect the
same syntax inside a recursive CTE.