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There are hacks in parse_coerce.c to push down a requested coercion to below any CollateExpr that may appear. However, we did that even if the requested data type is non-collatable, leading to an invalid expression tree in which CollateExpr is applied to a non-collatable type. The fix is just to drop the CollateExpr altogether, reasoning that it's useless. This bug is ten years old, dating to the original addition of COLLATE support. The lack of field complaints suggests that there aren't a lot of user-visible consequences. We noticed the problem because it would trigger an assertion in DefineVirtualRelation if the invalid structure appears as an output column of a view; however, in a non-assert build, you don't see a crash just a (subtly incorrect) complaint about applying collation to a non-collatable type. I found that by putting the incorrect structure further down in a view, I could make a view definition that would fail dump/reload, per the added regression test case. But CollateExpr doesn't do anything at run-time, so this likely doesn't lead to any really exciting consequences. Per report from Yulin Pei. Back-patch to all supported branches. Discussion: https://postgr.es/m/HK0PR01MB22744393C474D503E16C8509F4709@HK0PR01MB2274.apcprd01.prod.exchangelabs.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. 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/.