f2a69b352d
The SQL standard says that redundant unique constraints are disallowed, but we long ago decided that throwing an error would be too user-unfriendly, so we just drop redundant ones. The docs weren't very clear about that though, as this behavior was only explained for PRIMARY KEY vs UNIQUE, not UNIQUE vs UNIQUE. While here, I couldn't resist doing some copy-editing and markup-fixing on the adjacent text about INCLUDE options. Per bug #16767 from Matthias vd Meent. Discussion: https://postgr.es/m/16767-1714a2056ca516d0@postgresql.org
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/.