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0816fad6ee
After the planner was fixed to convert some IN/EXISTS subqueries into semijoins or antijoins, we had to prevent it from doing that in some cases where the plans risked getting much worse. The reason the plans got worse was that in the unoptimized implementation, subqueries could reference parameters from the outer query at any join level, and so full table scans could be avoided even if they were one or more levels of join below where the semi/anti join would be. Now that we have sufficient mechanism in the planner to handle such cases properly, it should no longer be necessary to play dumb here. This reverts commits07b9936a0fandcd1f0d04bf. The latter was a stopgap fix that wasn't really sufficiently analyzed at the time. Rather than just restricting ourselves to cases where the new join can be stacked on the right-hand input, we should also consider whether it can be stacked on the left-hand input.
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/.