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When checking a subquery's output expressions to see if it's safe to push down an upper-level qual, check_output_expressions() previously treated grouping Vars as opaque Vars. This implicitly assumed they were stable and scalar. However, a grouping Var's underlying expression corresponds to the grouping clause, which may be volatile or set-returning. If an upper-level qual references such an output column, pushing it down into the subquery is unsafe. This can cause strange results due to multiple evaluation of a volatile function, or introduce SRFs into the subquery's WHERE/HAVING quals. This patch teaches check_output_expressions() to look through grouping Vars to their underlying expressions. This ensures that any volatility or set-returning properties in the grouping clause are detected, preventing the unsafe pushdown. We do not need to recursively examine the Vars contained in these underlying expressions. Even if they reference outputs from lower-level subqueries (at any depth), those references are guaranteed not to expand to volatile or set-returning functions, because subqueries containing such functions in their targetlists are never pulled up. Backpatch to v18, where this issue was introduced. Reported-by: Eric Ridge <eebbrr@gmail.com> Diagnosed-by: Tom Lane <tgl@sss.pgh.pa.us> Author: Richard Guo <guofenglinux@gmail.com> Discussion: https://postgr.es/m/7900964C-F99E-481E-BEE5-4338774CEB9F@gmail.com Backpatch-through: 18 |
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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/18/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/18/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/.