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Formerly, when updating an auto-updatable view, or a relation with rules, if the original query had any data-modifying CTEs, the rewriter would rewrite those CTEs multiple times as RewriteQuery() recursed into the product queries. In most cases that was harmless, because RewriteQuery() is mostly idempotent. However, if the CTE involved updating an always-generated column, it would trigger an error because any subsequent rewrite would appear to be attempting to assign a non-default value to the always-generated column. This could perhaps be fixed by attempting to make RewriteQuery() fully idempotent, but that looks quite tricky to achieve, and would probably be quite fragile, given that more generated-column-type features might be added in the future. Instead, fix by arranging for RewriteQuery() to rewrite each CTE exactly once (by tracking the number of CTEs already rewritten as it recurses). This has the advantage of being simpler and more efficient, but it does make RewriteQuery() dependent on the order in which rewriteRuleAction() joins the CTE lists from the original query and the rule action, so care must be taken if that is ever changed. Reported-by: Bernice Southey <bernice.southey@gmail.com> Author: Bernice Southey <bernice.southey@gmail.com> Author: Dean Rasheed <dean.a.rasheed@gmail.com> Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us> Reviewed-by: Kirill Reshke <reshkekirill@gmail.com> Discussion: https://postgr.es/m/CAEDh4nyD6MSH9bROhsOsuTqGAv_QceU_GDvN9WcHLtZTCYM1kA@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/.