f41ab51573
In the spirit of 8d19d0e13, this patch teaches the planner about the principle that NullTest with !argisrow is fully equivalent to SQL's IS [NOT] DISTINCT FROM NULL. The parser already performs this transformation for literal NULLs. However, a DistinctExpr expression with one input evaluating to NULL during planning (e.g., via const-folding of "1 + NULL" or parameter substitution in custom plans) currently remains as a DistinctExpr node. This patch closes the gap for const-folded NULLs. It specifically targets the case where one input is a constant NULL and the other is a nullable non-constant expression. (If the other input were otherwise, the DistinctExpr node would have already been simplified to a constant TRUE or FALSE.) This transformation can be beneficial because NullTest is much more amenable to optimization than DistinctExpr, since the planner knows a good deal about the former and next to nothing about the latter. Author: Richard Guo <guofenglinux@gmail.com> Reviewed-by: Tender Wang <tndrwang@gmail.com> Discussion: https://postgr.es/m/CAMbWs49BMAOWvkdSHxpUDnniqJcEcGq3_8dd_5wTR4xrQY8urA@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/.