505c008ca3
0452b461bc made optimizer explore alternative orderings of group-by pathkeys. It eliminated preprocess_groupclause(), which was intended to match items between GROUP BY and ORDER BY. Instead, get_useful_group_keys_orderings() function generates orderings of GROUP BY elements at the time of grouping paths generation. The get_useful_group_keys_orderings() function takes into account 3 orderings of GROUP BY pathkeys and clauses: original order as written in GROUP BY, matching ORDER BY clauses as much as possible, and matching the input path as much as possible. Given that even before 0452b461b, preprocess_groupclause() could change the original order of GROUP BY clauses we don't need to consider it apart from ordering matching ORDER BY clauses. This commit restores preprocess_groupclause() to provide an ordering of GROUP BY elements matching ORDER BY before generation of paths. The new version of preprocess_groupclause() takes into account an incremental sort. The get_useful_group_keys_orderings() function now takes into 2 orderings of GROUP BY elements: the order generated preprocess_groupclause() and the order matching the input path as much as possible. Discussion: https://postgr.es/m/CAPpHfdvyWLMGwvxaf%3D7KAp-z-4mxbSH8ti2f6mNOQv5metZFzg%40mail.gmail.com Author: Alexander Korotkov Reviewed-by: Andrei Lepikhov, Pavel Borisov
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/.