Re: psql: Add command to use extended query protocol

On Mon, Nov 7, 2022 at 4:12 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:

> Corey Huinker <corey.huinker@gmail.com> writes:
> > I thought about basically reserving the \$[0-9]+ space as bind variables,
> > but it is possible, though unlikely, that users have been naming their
> > variables like that.
>
> Don't we already reserve that syntax as Params?  Not sure whether there
> would be any conflicts versus Params, but these are definitely not legal
> as SQL identifiers.
>
>                         regards, tom lane
>

I think Pavel was hinting at something like:

\set $1 foo
\set $2 123
UPDATE mytable SET value = $1 WHERE id = $2;

Which wouldn't step on anything, because I tested it, and \set $1 foo
already returns 'Invalid variable name "$1"'.

So far, there seem to be two possible variations on how to go about this:

1. Have special variables or a variable namespace that are known to be bind
variables. So long as one of them is defined, queries are sent using
extended query protocol.
2. Bind parameters one-time-use, applied strictly to the query currently in
the buffer in positional order, and once that query is run their
association with being binds is gone.

Each has its merits, I guess it comes down to how much we expect users to
want to re-use some or all the bind params of the previous query.