90893c7b7c
EXPLAIN failed to deal with varno-0 Vars that are made by prepunion.c and can survive into a finished plan in the case where a provably empty set operation is replaced by a dummy Result (which is possible since03d40e4b5). Commit928df067dtried to fix this, but it was a couple bricks shy of a load. First, it only dealt with varno-0 Vars at the top level of the Result's tlist, but they could be buried under coercion expressions. Fix that by doing a recursive mutation. Second, it always replaced varno 0 with varno 1, but that's just wrong: the Result might represent a group of setop leaf queries that do not include the leftmost leaf. That led to displaying the wrong variable(s) as outputs of the Result, risking confusion. Fortunately, we can get the actual child relids from the recently-added Result.relids field, and use that to discover the leftmost child represented by the Result. This was found while discussing bug #19742, but it's really an independent issue. Author: shihao zhong <zhong950419@gmail.com> Co-authored-by: Tom Lane <tgl@sss.pgh.pa.us> Discussion: https://postgr.es/m/CAGRkXqTFwygKmjLG_Y=kbXRHsePFmD6k+qrzVLP4_KrG+-=oRg@mail.gmail.com Backpatch-through: 19
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.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/installation.html.
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/.