> On 15/08/2023 10:49 CEST [Quipsy] Markus Karg <karg@xxxxxxxxx> wrote: > > Hello PostgreSQL Community, > > I like to store just a single bit but that can be either 1 or 0, so I tried > to do this: > > CREATE TABLE T (c BIT); > INSERT INTO T VALUES (1); > -- I MUST NOT change both lines in any way as these are part of a third-party application! > > Unfortunately this tells me: > > column "c" is of type bit but expression is of type integer > > So I logged in as a cluster admin and I tried this: > > CREATE CAST (integer AS bit) WITH INOUT AS IMPLICIT; > > Unfortunately that tells me: > > cast from type integer to type bit already exists > > This is confusing! Apparently PostgreSQL 15.3 comes with the needed cast > out-of-the-box but it does not apply it? This is confusing! > > What is my fault? The built-in cast is explicit (castcontext = 'e'): =# SELECT * FROM pg_cast WHERE castsource = 'int'::regtype AND casttarget = 'bit'::regtype; oid | castsource | casttarget | castfunc | castcontext | castmethod -------+------------+------------+----------+-------------+------------ 10186 | 23 | 1560 | 1683 | e | f (1 row) It's not possible to drop that cast and replace it with a custom one: =# DROP CAST (int AS bit); ERROR: cannot drop cast from integer to bit because it is required by the database system You could create a custom domain if you're only interested in values 0 and 1 and don't use bit string functions. The search path must be changed so that domain bit overrides pg_catalog.bit: =# CREATE SCHEMA xxx; =# CREATE DOMAIN xxx.bit AS int; =# SET search_path = xxx, pg_catalog; =# CREATE TABLE t (c bit); =# INSERT INTO t VALUES (1); INSERT 0 1 But I would do that only if the third-party code cannot be tweaked because the custom domain could be confusing. It's also prone to errors as it relies on a specific search path order. Also make sure that regular users cannot create objects in schema xxx that would override objects in pg_catalog. -- Erik
