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Since commit 8f321bd16c functional dependencies can handle IN clauses, which however introduced a possible (and surprising) inconsistency, because IN clauses may be expressed as an OR clause, which are still considered incompatible. For example a IN (1, 2, 3) may be rewritten as (a = 1 OR a = 2 OR a = 3) The IN clause will work fine with functional dependencies, but the OR clause will force the estimation to fall back to plain per-column estimates, possibly introducing significant estimation errors. This commit recognizes OR clauses equivalent to an IN clause (when all arugments are compatible and reference the same attribute) as a special case, compatible with functional dependencies. This allows applying functional dependencies, just like for IN clauses. This does not eliminate the difference in estimating the clause itself, i.e. IN clause and OR clause still use different formulas. It would be possible to change that (for these special OR clauses), but that's not really about extended statistics - it was always like this. Moreover the errors are usually much smaller compared to ignoring dependencies. Author: Tomas Vondra Reviewed-by: Dean Rasheed Discussion: https://www.postgresql.org/message-id/flat/13902317.Eha0YfKkKy%40pierred-pdoc
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/.