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If we have a RestrictInfo that mentions both the removal-candidate relation and the outer join's relid, then that is a pushed-down condition not a join condition, so it should be grounds for deciding that we can't remove the outer join. In commit 2489d76c4, I'd blindly included the OJ's relid into "joinrelids" as per the new standard convention, but the checks of attr_needed and ph_needed should only allow the join's input rels to be mentioned. Having done that, the check for references in pushed-down quals a few lines further down should be redundant. I left it in place as an Assert, though. While researching this I happened across a couple of comments that worried about the effects of update_placeholder_eval_levels. That's gone as of b448f1c8d, so we can remove some worry. Per bug #17769 from Robins Tharakan. The submitted test case triggers this more or less accidentally because we flatten out a LATERAL sub-select after we've done join strength reduction; if we did that in the other order, this problem would be masked because the outer join would get simplified to an inner join. To ensure that the committed test case will continue to test what it means to even if we make that happen someday, use a test clause involving COALESCE(), which will prevent us from using it to do join strength reduction. Patch by me, but thanks to Richard Guo for initial investigation. Discussion: https://postgr.es/m/17769-e4f7a5c9d84a80a7@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. 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/.