Re: [NOVICE] opr_charset rule in gram.y

On Tue, Mar 7, 2017 at 4:30 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Neha Khatri <nehakhatri5(at)gmail(dot)com> writes:
> > I was going through the grammer rule for Character types in gram.y and
> > found an optional sub rule in is "opt_charset"
>
> This question seems quite off-topic for pgsql-novice, so I've redirected
> it to pgsql-hackers.
>

Thanks for appropriately categorizing. I was not sure.

> > CharacterWithLength: character '(' Iconst ')' opt_charset
> > {
> > if (($5 != NULL) && (strcmp($5, "sql_text") != 0))
> > $1 = psprintf("%s_%s", $1, $5);
> >
> > $$ = SystemTypeName($1);
>
> > I would like to understand how opt_charset would get used in real
> > applications. I tried to make use of it but results in failure:
>
> > postgres=# create table testchar (c1 char(5) character set utf8);
> > ERROR: type "pg_catalog.bpchar_utf8" does not exist
> > LINE 1: create table testchar (c1 char(5) character set utf8);
>
> > There does not seem to be any documentation available about this optional
> > parameter in the documents for Character data type( at least I could not
> > find any).
>
> Some digging in the git history shows that opt_charset was introduced in
> commit f10b63923 (in 1997!), and the current interpretation as
> "typename_charsetname" appeared in commit 3e1beda2c. Neither commit
> adds any user documentation or even mentions fooling with character type
> declarations in its commit message. I think that this must have been
> work-in-progress that Tom Lockhart left behind when he dropped out of
> the project circa 2002.
>
> Since there are no datatypes matching the "typename_charsetname" naming
> pattern, and today we'd be unlikely to accept an implementation based on
> that approach even if someone wrote one, my inclination is just to rip out
> this code. Maybe we could leave behind the no-op case that allows
> "CHARACTER SET SQL_TEXT", but I don't really see the point, since we've
> never documented supporting any such syntax.
>
> Ok, understood, good historical detail.. Will go through
"typename_charsetname"
to understand the concept. Then may be come up with the cleanup patch.

Thanks and Regards,
Neha