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If a Var was used only in a GROUP BY expression, the previous implementation would include the Var by itself (as well as the expression) in the generated targetlist. This wouldn't affect the efficiency of the scan/join part of the plan at all, but it could result in passing unnecessarily-wide rows through sorting and grouping steps. It turns out to take only a little more code, and not noticeably more time, to generate a tlist without such redundancy, so let's do that. Per a recent gripe from HarmeekSingh Bedi.
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: http://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. Changes between all PostgreSQL releases are recorded in the file HISTORY. 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 http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.