4f1124548f
When creating merge or hash join plans in createplan.c, the merge or hash clauses may need to get commuted to ensure that the outer var is on the left and the inner var is on the right if they are not already in the expected form. This requires that their operators have commutators. Failing to find a commutator at this stage would result in 'ERROR: could not find commutator for operator xxx', with no opportunity to select an alternative plan. Typically, this is not an issue because mergejoinable or hashable operators are expected to always have valid commutators. But in some artificial cases this assumption may not hold true. Therefore, here in this patch we check the validity of commutators for clauses in the form "inner op outer" when selecting mergejoin/hash clauses, and consider a clause unusable for the current pair of outer and inner relations if it lacks a commutator. There are not (and should not be) any such operators built into Postgres that are mergejoinable or hashable but have no commutators; so we leverage the alias type 'int8alias1' created in equivclass.sql to build the test case. This is why the test case is included in equivclass.sql rather than in join.sql. Although this is arguably a bug fix, it cannot be reproduced without installing an incomplete opclass, which is unlikely to happen in practice, so no back-patch. Reported-by: Alexander Pyhalov Author: Richard Guo Reviewed-by: Tom Lane Discussion: https://postgr.es/m/c59ec04a2fef94d9ffc35a9b17dfc081@postgrespro.ru |
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README.md
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/.