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Currently, if operator_predicate_proof() is given an operator clause like "something op NULL", it just throws up its hands and reports it can't prove anything. But we can often do better than that, if the operator is strict, because then we know that the clause returns NULL overall. Depending on whether we're trying to prove or refute something, and whether we need weak or strong semantics for NULL, this may be enough to prove the implication, especially when we rely on the standard rule that "false implies anything". In particular, this lets us do something useful with questions like "does X IN (1,3,5,NULL) imply X <= 5?" The null entry in the IN list can effectively be ignored for this purpose, but the proof rules were not previously smart enough to deduce that. This patch is by me, but it owes something to previous work by Amit Langote to try to solve problems of the form mentioned. Thanks also to Emre Hasegeli and Ashutosh Bapat for review. Discussion: https://postgr.es/m/3bad48fc-f257-c445-feeb-8a2b2fb622ba@lab.ntt.co.jp
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/.