ca70bdaefe
As a result of some long-ago quick hacks, the SIMILAR TO operator and the corresponding flavor of substring() interpreted "ESCAPE NULL" as selecting the default escape character '\'. This is both surprising and not per spec: the standard is clear that these functions should return NULL for NULL input. Additionally, because of inconsistency of the strictness markings of 3-argument substring() and similar_escape(), the planner could not inline the SQL definition of substring(), resulting in a substantial performance penalty compared to the underlying POSIX substring() function. The simplest fix for this would be to change the strictness marking of similar_escape(), but if we do that we risk breaking existing views that depend on that function. Hence, leave similar_escape() as-is as a compatibility function, and instead invent a new function similar_to_escape() that comes in two strict variants. There are a couple of other behaviors in this area that are also not per spec, but they are documented and seem generally at least as sane as the spec's definition, so leave them alone. But improve the documentation to describe them fully. Patch by me; thanks to Álvaro Herrera and Andrew Gierth for review and discussion. Discussion: https://postgr.es/m/14047.1557708214@sss.pgh.pa.us |
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README
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/.