Re: [PATCH] docs: document N'...' national character string literal syntax

On 2026-02-02 16:05 +0100, Hoda Salim wrote:
> This patch documents the N'...' national character string literal
> syntax, which has been supported by PostgreSQL but was previously
> undocumented.
>
> The documentation explains:
> - What the syntax is (N'hello')
> - What the SQL standard specifies (implementation-defined national
> character set)
> - What PostgreSQL actually does (treats it as a cast to character type)
> - Why it exists (compatibility with SQL migrated from other databases)
>
> I verified the documentation builds without errors.

+1

I brought up the missing documentation before [1], but wasn't sure at
the time if Postgres conforms to the SQL standard (mainly because of
[2]). Now I see that [3] already claims to support national character
(F421). That entry was commented with "syntax accepted" until commit
35223af0579. I read that as "fully supported" now.

> + <productname>PostgreSQL</productname> does not implement a separate
> + national character set; it treats <literal>N'...'</literal> as
> + equivalent to a regular string constant cast to the
> + <type>character</type> type, that is, <literal>'...'::character</literal>,
> + using the database's character set.

nchar is an alias of bpchar. There's no cast to char behind the scenes
since that would truncate the string:

select n'foo', 'foo'::character;
bpchar | bpchar
--------+--------
foo | f
(1 row)

Should we also mention the nchar alias in [4]?

[1] https://www.postgresql.org/message-id/om3g7p7u3ztlrdp4tfswgulavljgn2fe6u2agk34mrr65dffuu%40cpzlzuv6flko
[2] https://www.postgresql.org/message-id/1275895438.1849.1.camel@fsopti579.F-Secure.com
[3] https://www.postgresql.org/docs/current/features-sql-standard.html
[4] https://www.postgresql.org/docs/current/datatype-character.html

--
Erik Wienhold