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I removed the delay_upper_joins mechanism in commit b448f1c8d, reasoning that it was only needed when we have a single-table (SELECT ... WHERE) as the immediate RHS child of a left join, and we could get rid of that by hoisting the WHERE condition into the parent join's quals. However that new code missed a case: we could have "foo LEFT JOIN ((SELECT ... WHERE) LEFT JOIN bar)", and if the two left joins can be commuted then we now have the problematic query shape. We can fix this too easily enough, by allowing the syntactically-lower left join to pass through its parent qual location pointer recursively. That lets prepjointree.c discard the SELECT by temporarily hoisting the WHERE condition into the ancestor join's qual. Per bug #17978 from Zuming Jiang. Discussion: https://postgr.es/m/17978-12f3d93a55297266@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/.