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When considering functional dependencies during selectivity estimation, it's not necessary to bother with selecting the best extended statistic object and then use just dependencies from it. We can simply consider all applicable functional dependencies at once. This means we need to deserialie all (applicable) dependencies before applying them to the clauses. This is a bit more expensive than picking the best statistics and deserializing dependencies for it. To minimize the additional cost, we ignore statistics that are not applicable. Author: Tomas Vondra Reviewed-by: Mark Dilger Discussion: https://postgr.es/m/20191028152048.jc6pqv5hb7j77ocp@development
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/.