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eval_const_expressions sometimes produced RelabelType nodes that were useless because they just relabeled an expression to the same exposed type it already had. This is worth avoiding because it can cause two equivalent expressions to not be equal(), preventing recognition of useful optimizations. In the test case added here, an unpatched planner fails to notice that the "sqli = constant" clause renders a sort step unnecessary, because one code path produces an extra RelabelType and another doesn't. Fix by ensuring that eval_const_expressions_mutator's T_RelabelType case will not add in an unnecessary RelabelType. Also save some code by sharing a subroutine with the effectively-equivalent cases for CollateExpr and CoerceToDomain. (CollateExpr had no bug, and I think that the case couldn't arise with CoerceToDomain, but it seems prudent to do the same check for all three cases.) Back-patch to v12. In principle this has been wrong all along, but I haven't seen a case where it causes visible misbehavior before v12, so refrain from changing stable branches unnecessarily. Per investigation of a report from Eric Gillum. Discussion: https://postgr.es/m/CAMmjdmvAZsUEskHYj=KT9sTukVVCiCSoe_PBKOXsncFeAUDPCQ@mail.gmail.com |
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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. 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/.