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I missed a restriction that commit f4abd0241de20d5d6a79b84992b9e88603d44134 should have enforced: we can't pull up an empty-FROM subquery if it's under an outer join, because then we'd need to wrap its output columns in PlaceHolderVars. As the code currently stands, the PHVs end up with empty relid sets, which doesn't work (and is correctly caught by an Assert). It's possible that this could be fixed by assigning the PHVs the relid sets of the parent FromExpr/JoinExpr, but getting that to work is more complication than I care to add right now; indeed it's likely that we'll never bother, since pulling up empty-FROM subqueries is a rather marginal optimization anyway. Per report from Andreas Seltenreich. Back-patch to 9.5 where the faulty code was added.
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/.