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When a join alias Var with nonempty varnullingrels expands to an expression that cannot carry the nullingrels itself, such as the RowExpr of a whole-row Var, add_nullingrels_if_needed() wraps it in a PlaceHolderVar. The choice of the PHV's phrels had several problems. First, phrels was taken from all Vars in the expression. If a LATERAL subquery within the join has been pulled up, the expression can contain lateral references to rels outside the join, so the PHV could be evaluated above the outer join that is supposed to null it. This gave wrong results, or "wrong phnullingrels" errors. Second, for a variable-free expression we fell back to the join's relids but removed the join's own outer-join relid. That leaves a set spanning both sides of the outer join without the join itself, which can make the PHV look nullable by that join and cause "wrong phnullingrels" errors. Third, that fallback raised "unsupported join alias expression" when the Var is an outer reference from a subquery. The restriction is unnecessary: every planner caller passes root->parse as the query, so the Var always belongs to root->parse regardless of its varlevelsup. To fix, restrict phrels to the rels within the join, and if nothing is left, evaluate the PHV at the join including its outer-join relid, at any varlevelsup. Add an assertion that the query is root->parse. Author: Richard Guo <guofenglinux@gmail.com> Discussion: https://postgr.es/m/CAMbWs49q_gvoeOoF0+KZ-DpQaDb=nGFfSgrz2V_n1_64L4ZNVQ@mail.gmail.com Backpatch-through: 16
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/.