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pull_up_simple_subquery() rechecks is_simple_subquery() after pulling up the subquery's own subqueries, but it flattened join alias Vars in the subquery's targetlist only after that, and never in its quals. A join alias Var within the subquery, such as a whole-row Var of a join, can expand to an expression containing lateral references to the outer query once the join's inputs have been pulled up, and until it is flattened is_simple_subquery() cannot see them. We could thus pull up a LATERAL subquery whose targetlist or quals reference rels outside the lowest outer join above it. This leads to assertion failures in distribute_qual_to_rels() or "wrong phnullingrels" errors, and in some cases to wrong query results, where rows that should have been preserved by an outer join above the subquery are discarded. To fix, flatten join alias Vars in the targetlist, and in the jointree quals if the subquery is LATERAL, before the recheck. If the recheck fails, the flattened copy is discarded along with the rest of the modified subquery, so no harm is done. Back-patch to all supported branches, as this can lead to wrong query results. Author: Richard Guo <guofenglinux@gmail.com> Reviewed-by: Tatsuya Kawata <kawatatatsuya0913@gmail.com> Discussion: https://postgr.es/m/CAMbWs48GFZ=3Bjc1ug9JRsB0Qupg+CGcb9js5vmTM6kY2OGWOg@mail.gmail.com Backpatch-through: 14
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: https://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 https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.