926fa801ac
This feature was added a long time ago, in 7c1e67bd5 and eb121ba2c, but never documented in any user-facing way. (Documentation added in 6126d3e70 was commented out almost immediately, in 8272fc3f7.) That's because, while this syntax is defined by SQL:99, our implementation is only vaguely related to the standard's semantics. The standard appears to intend a run-time not parse-time test, and it definitely intends that the test should understand subtype relationships. No one has stepped up to fix that in the intervening years, but people keep coming across the code and asking why it's not documented. Let's just get rid of it: if anyone ever wants to make it work per spec, they can easily recover whatever parts of this code are still of value from our git history. If there's anyone out there who's actually using this despite its undocumented status, they can switch to using pg_typeof() instead, eg. "pg_typeof(something) = 'mytype'::regtype". That gives essentially the same semantics as what our IS OF code did. (We didn't have that function last time this was discussed, or we would have ripped out IS OF then.) Discussion: https://postgr.es/m/CAKFQuwZ2pTc-DSkOiTfjauqLYkNREeNZvWmeg12Q-_69D+sYZA@mail.gmail.com Discussion: https://postgr.es/m/BAY20-F23E9F2B4DAB3E4E88D3623F99B0@phx.gbl Discussion: https://postgr.es/m/3E7CF81D.1000203@joeconway.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/.