Re: proposal: psql \setfileref

Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
> [ psql-setfileref-2016-10-11.patch ]

I haven't been paying any attention to this thread, but I got around to
looking at it finally. I follow the idea of wanting to be able to shove
the contents of a file into a query literal, but there isn't much else
that I like about this patch. In particular:

* I really dislike the notion of keying the behavior to a special type of
psql variable. psql variables are untyped at the moment, and if we were
going to introduce typing, this wouldn't be what I'd want to use it for.
I really don't want to introduce typing and then invent one-off,
unextensible syntax like '^' prefixes to denote what type a variable is.

Aside from being conceptually a mess, I don't even find it particularly
convenient. In the shell, if you want to source from a file, you write
"<filename". You aren't compelled to assign the filename to a variable
and then write "<$filename" ... although you can if that's actually
helpful.

Going by the notion of driving it off syntax not variable type, I'd
suggest that we extend the colon-variablename syntax to indicate
desire to read a file. :<filename< is one pretty obvious idea.
Maybe we could use :<:variablename< to indicate substituting the
content of a variable as the file name to read.

* I'm a bit queasy about the idea of automatically switching over to
parameterized queries when we have one of these things in the query.
I'm afraid that that will have user-visible consequences, so I would
rather that psql not do that behind the user's back. Plus, that assumes
a fact not in evidence, namely that you only ever want to insert data
and not code this way. (If \i were more flexible, that objection would
be moot, but you can't source just part of a query from \i AFAIK.)
There might be something to be said for a psql setting that controls
whether to handle colon-insertions this way, and make it apply to
the existing :'var' syntax as well as the filename syntax.

* I find the subthread about attaching this to COPY to be pretty much of
a red herring. What would that do that you can't do today with \copy?

regards, tom lane