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Although joinaliasvars lists coming out of the parser are quite simple, those lists can contain arbitrarily complex expressions after subquery pullup. We do not perform expression preprocessing on them, meaning that expressions in those lists will not meet the expectations of later phases of the planner (for example, that they do not contain SubLinks). This had been thought pretty harmless, since we don't intentionally touch those lists in later phases --- but Andreas Seltenreich found a case in which adjust_appendrel_attrs() could recurse into a joinaliasvars list and then die on its assertion that it never sees a SubLink. We considered a couple of localized fixes to prevent that specific case from looking at the joinaliasvars lists, but really this seems like a generic hazard for all expression processing in the planner. Therefore, probably the best answer is to delete the joinaliasvars lists from the parsetree at the end of expression preprocessing, so that there are no reachable expressions that haven't been through preprocessing. The case Andreas found seems to be harmless in non-Assert builds, and so far there are no field reports suggesting that there are user-visible effects in other cases. I considered back-patching this anyway, but it turns out that Andreas' test doesn't fail at all in 9.4-9.6, because in those versions adjust_appendrel_attrs contains code (added in commit 842faa714 and removed again in commit 215b43cdc) to process SubLinks rather than complain about them. Barring discovery of another path by which unprocessed joinaliasvars lists can cause trouble, the most prudent compromise seems to be to patch this into v10 but not further. Patch by me, with thanks to Amit Langote for initial investigation and review. Discussion: https://postgr.es/m/87r2tvt9f1.fsf@ansel.ydns.eu
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. PostgreSQL has many language interfaces, many of which are listed here: https://www.postgresql.org/download 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 may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.