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Previously, we left such literals alone if the query or subquery had no properties forcing a type decision to be made (such as an ORDER BY or DISTINCT clause using that output column). This meant that "unknown" could be an exposed output column type, which has never been a great idea because it could result in strange failures later on. For example, an outer query that tried to do any operations on an unknown-type subquery output would generally fail with some weird error like "failed to find conversion function from unknown to text" or "could not determine which collation to use for string comparison". Also, if the case occurred in a CREATE VIEW's query then the view would have an unknown-type column, causing similar failures in queries trying to use the view. To fix, at the tail end of parse analysis of a query, forcibly convert any remaining "unknown" literals in its SELECT or RETURNING list to type text. However, provide a switch to suppress that, and use it in the cases of SELECT inside a set operation or INSERT command. In those cases we already had type resolution rules that make use of context information from outside the subquery proper, and we don't want to change that behavior. Also, change creation of an unknown-type column in a relation from a warning to a hard error. The error should be unreachable now in CREATE VIEW or CREATE MATVIEW, but it's still possible to explicitly say "unknown" in CREATE TABLE or CREATE (composite) TYPE. We want to forbid that because it's nothing but a foot-gun. This change creates a pg_upgrade failure case: a matview that contains an unknown-type column can't be pg_upgraded, because reparsing the matview's defining query will now decide that the column is of type text, which doesn't match the cstring-like storage that the old materialized column would actually have. Add a checking pass to detect that. While at it, we can detect tables or composite types that would fail, essentially for free. Those would fail safely anyway later on, but we might as well fail earlier. This patch is by me, but it owes something to previous investigations by Rahila Syed. Also thanks to Ashutosh Bapat and Michael Paquier for review. Discussion: https://postgr.es/m/CAH2L28uwwbL9HUM-WR=hromW1Cvamkn7O-g8fPY2m=_7muJ0oA@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. PostgreSQL has many language interfaces, many of which are listed here: http://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 http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.