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Tom Lane f15821eefd Allow join removal in some cases involving a left join to a subquery. 
We can remove a left join to a relation if the relation's output is
provably distinct for the columns involved in the join clause (considering
only equijoin clauses) and the relation supplies no variables needed above
the join.  Previously, the join removal logic could only prove distinctness
by reference to unique indexes of a table.  This patch extends the logic
to consider subquery relations, wherein distinctness might be proven by
reference to GROUP BY, DISTINCT, etc.

We actually already had some code to check that a subquery's output was
provably distinct, but it was hidden inside pathnode.c; which was a pretty
bad place for it really, since that file is mostly boilerplate Path
construction and comparison.  Move that code to analyzejoins.c, which is
arguably a more appropriate location, and is certainly the site of the
new usage for it.

David Rowley, reviewed by Simon Riggs
 		2014-07-15 21:12:43 -04:00
config Remove some useless code in the configure script. 2014-07-01 17:51:53 -04:00
contrib pg_upgrade: Fix spacing in help output 2014-07-15 15:08:16 -04:00
doc doc: Put new options in right order on reference pages 2014-07-15 15:08:16 -04:00
src Allow join removal in some cases involving a left join to a subquery. 2014-07-15 21:12:43 -04:00
.dir-locals.el Update Emacs configuration 2013-08-13 20:08:44 -04:00
.gitattributes gitattributes: Make syntax compatible with older Git versions 2013-11-12 21:58:46 -05:00
.gitignore Add *.pot to .gitignore 2013-10-19 10:56:52 -04:00
COPYRIGHT Update copyright for 2014 2014-01-07 16:05:30 -05:00
GNUmakefile.in Add TAP tests for client programs 2014-04-14 21:33:46 -04:00
HISTORY Improve text of stub HISTORY file. 2014-02-12 18:16:17 -05:00
Makefile Allow make check in PL directories 2011-02-15 06:52:12 +02:00
README Don't generate plain-text HISTORY and src/test/regress/README anymore. 2014-02-10 20:48:04 -05:00
README.git Don't generate plain-text HISTORY and src/test/regress/README anymore. 2014-02-10 20:48:04 -05:00
aclocal.m4 Remove cvs keywords from all files. 2010-09-20 22:08:53 +02:00
configure Move check for SSL_get_current_compression to run on mingw 2014-07-15 22:02:46 +02:00
configure.in Move check for SSL_get_current_compression to run on mingw 2014-07-15 22:02:46 +02:00

README 

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.  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/.