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We can simplify FieldSelect on a whole-row Var into a plain Var for the selected field. However, we should copy the whole-row Var's varnullingrels when we do so, because the new Var is clearly nullable by exactly the same rels as the original. Failure to do this led to errors like "wrong varnullingrels (b) (expected (b 3)) for Var 2/2". Richard Guo, per bug #18184 from Marian Krucina. Back-patch to v16 where varnullingrels was introduced. Discussion: https://postgr.es/m/18184-5868dd258782058e@postgresql.org
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. 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, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.