The following bug has been logged on the website:
Bug reference: 16255
Logged by: Robert Ford
Email address: robfordww@gmail.com
PostgreSQL version: 12.1
Operating system: Windows
Description:
I have an simple CTE expression with group by and a string_aggr() function,
and Postgresql seems to materialize it anyhow, even if 'not materialized' is
instructed. I can't see that this is documented behaviour.