10c4fe074a
The COALESCE function returns the first of its arguments that is not null. When an argument is proven non-null, if it is the first non-null-constant argument, the entire COALESCE expression can be replaced by that argument. If it is a subsequent argument, all following arguments can be dropped, since they will never be reached. Currently, we perform this simplification only for Const arguments. This patch extends the simplification to support any expression that can be proven non-nullable. This can help avoid the overhead of evaluating unreachable arguments. It can also lead to better plans when the first argument is proven non-nullable and replaces the expression, as the planner no longer has to treat the expression as non-strict, and can also leverage index scans on the resulting expression. There is an ensuing plan change in generated_virtual.out, and we have to modify the test to ensure that it continues to test what it is intended to. Author: Richard Guo <guofenglinux@gmail.com> Reviewed-by: Tender Wang <tndrwang@gmail.com> Reviewed-by: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org> Reviewed-by: David Rowley <dgrowleyml@gmail.com> Reviewed-by: Matheus Alcantara <matheusssilv97@gmail.com> Discussion: https://postgr.es/m/CAMbWs49UhPBjm+NRpxerjaeuFKyUZJ_AjM3NBcSYK2JgZ6VTEQ@mail.gmail.com
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.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/installation.html.
The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.