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This change prevents us from doing inappropriate subquery flattening in cases such as dangerous functions hidden inside a sub-SELECT in the targetlist of another sub-SELECT. That could result in unexpected behavior due to multiple evaluations of a volatile function, as in a recent complaint from Etienne Dube. It's been questionable from the very beginning whether these functions should look into subqueries (as noted in their comments), and this case seems to provide proof that they should. Because the new code only descends into SubLinks, not SubPlans or InitPlans, the change only affects the planner's behavior during prepjointree processing and not later on --- for example, you can still get it to use a volatile function in an indexqual if you wrap the function in (SELECT ...). That's a historical behavior, for sure, but it's reasonable given that the executor's evaluation rules for subplans don't depend on whether there are volatile functions inside them. In any case, we need to constrain the behavioral change as narrowly as we can to make this reasonable to back-patch. |
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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/.