On Thu, 2023-11-16 at 22:38 -0500, Tom Lane wrote:
> That line of argument also leads to the conclusion that it'd be
> okay to expose info about the ordering of the CTE result to the
> upper planner. [...] The fence is sort of one-way
> in this line of thinking: information can propagate up to the outer
> planner level, but not down into the CTE plan.
>
> Thoughts?
That agrees with my intuition about MATERIALIZED CTEs.
I think of them as "first calculate the CTE, then calculate the
rest of the query" or an ad-hoc temporary table for the duration
of a query. I would expect the upper planner to know estimates
and other data about the result of the CTE.
Yours,
Laurenz Albe