931766aaec
If, after removal of useless null-constant arguments, a CoalesceExpr has exactly one remaining argument, we can just take that argument as the result, without bothering to wrap a new CoalesceExpr around it. This isn't likely to produce any great improvement in runtime per se, but it can lead to better plans since the planner no longer has to treat the expression as non-strict. However, there were a few regression test cases that intentionally wrote COALESCE(x) as a shorthand way of creating a non-strict subexpression. To avoid ruining the intent of those tests, write COALESCE(x,x) instead. (If anyone ever proposes de-duplicating COALESCE arguments, we'll need another iteration of this arms race. But it seems pretty unlikely that such an optimization would be worthwhile.) Author: Maksim Milyutin <maksim.milyutin@tantorlabs.ru> Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us> Discussion: https://postgr.es/m/8e8573c3-1411-448d-877e-53258b7b2be0@tantorlabs.ru
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/.