f00484c170
query_is_distinct_for() is intended to determine whether a query never returns duplicates of the specified columns. For queries using grouping sets, if there are no grouping expressions, the query may contain one or more empty grouping sets. The goal is to detect whether there is exactly one empty grouping set, in which case the query would return a single row and thus be distinct. The previous logic in query_is_distinct_for() was incomplete because the check was insufficiently thorough and could return false when it could have returned true. It failed to consider cases where the DISTINCT clause is used on the GROUP BY, in which case duplicate empty grouping sets are removed, leaving only one. It also did not correctly handle all possible structures of GroupingSet nodes that represent a single empty grouping set. To fix, add a check for the groupDistinct flag, and expand the query's groupingSets tree into a flat list, then verify that the expanded list contains only one element. No backpatch as this could result in plan changes. Author: Richard Guo <guofenglinux@gmail.com> Reviewed-by: David Rowley <dgrowleyml@gmail.com> Discussion: https://postgr.es/m/CAMbWs480Z04NtP8-O55uROq2Zego309+h3hhaZhz6ztmgWLEBw@mail.gmail.com
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/.