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examine_simple_variable() left this as an unimplemented case years ago, with the result that plans for queries involving un-flattened CTEs might be much stupider than necessary. It's not hard to extend the existing logic for RTE_SUBQUERY cases to also be able to drill down into CTEs, so let's do that. There was some discussion of whether this patch breaks the idea of a MATERIALIZED CTE being an optimization fence. We concluded it's okay, because we already allow the outer planner level to see the estimated width and rowcount of the CTE result, and letting it see column statistics too seems fairly equivalent. Basically, what we expect of the optimization fence is that the outer query should not affect the plan chosen for the CTE query. Once that plan is chosen, it's okay for the outer planner level to make use of whatever information we have about it. Jian Guo and Tom Lane, per complaint from Hans Buschmann Discussion: https://postgr.es/m/4504e67078d648cdac3651b2960da6e7@nidsa.net
PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.