Re: Variable substitution in psql backtick expansion

From: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Daniel Verite <daniel(at)manitou-mail(dot)org>, PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Variable substitution in psql backtick expansion
Date: 2017-04-03 19:24:39
Message-ID: alpine.DEB.2.20.1704032118250.23892@lancre
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Hello Tom,

>> \if [select current_setting('server_version_num')::int < 110000]
>
> I really dislike this syntax proposal.

> It would get us into having to count nested brackets, and distinguish
> quoted from unquoted brackets, and so on ... and for what? It's not
> really better than
>
> \if sql select 1 from pg_catalog.pg_extension where extname='pgcrypto'

Hmmm. On the positive side, it looks more expression-like, and it allows
to think of handling a multi-line expression on day.

ISTM that the lexer already counts parentheses, so maybe using external
parentheses might work without much effort?

> (ie, "\if sql ...text to send to server...").
>
> If you're worried about shaving keystrokes, make the "select" be implicit.
> That would be particularly convenient for the common case where you're
> just trying to evaluate a boolean expression with no table reference.

I'm looking for a solution to avoid the suggested "sql" prefix, because "I
really dislike this proposal", as you put it.

--
Fabien.

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