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f4f195d15c
This case wasn't thought through sufficiently in commit 100340e2d. It's true that the FK proves that every outer row has a match in the inner table, but we forgot that some of the inner rows might be filtered away by WHERE conditions located within the semijoin's RHS. If the RHS is just one table, we can reasonably take the semijoin selectivity as equal to the fraction of the referenced table's rows that are expected to survive its restriction clauses. If the RHS is a join, it's not clear how much of the referenced table might get through the join, so fall back to the same rule we were already using for other outer-join cases: use the minimum of the regular per-clause selectivity estimates. This gives the same result as if we hadn't considered the FK at all when there's a single FK column, but it should still help for multi-column FKs, which is the case that 100340e2d is really meant to help with. Back-patch to 9.6 where the previous commit came in. Discussion: https://postgr.es/m/16149.1481835103@sss.pgh.pa.us
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: http://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 http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.