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PG type coercions are generally strict, ie a NULL input must produce a NULL output (or, in domain cases, possibly an error). The planner's understanding of that was a bit incomplete though, so improve it: * Teach contain_nonstrict_functions() that CoerceViaIO can always be considered strict. Previously it believed that only if the underlying I/O functions were marked strict, which is often but not always true. * Teach clause_is_strict_for() that CoerceViaIO, ArrayCoerceExpr, ConvertRowtypeExpr, CoerceToDomain can all be considered strict. Previously it knew nothing about any of them. The main user-visible impact of this is that IS NOT NULL predicates can be proven to hold from expressions involving casts in more cases than before, allowing partial indexes with such predicates to be used without extra pushups. This reduces the surprise factor for users, who may well be used to ordinary (function-call-based) casts being known to be strict. Per a gripe from Samuel Williams. This doesn't rise to the level of a bug, IMO, so no back-patch. Discussion: https://postgr.es/m/27571.1550617881@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: 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/.