Horton

Re: Variable substitution in psql backtick expansion

Fabien COELHO <coelho@cri.ensmp.fr>

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From: Fabien COELHO <coelho@cri.ensmp.fr>
To: Daniel Verite <daniel@manitou-mail.org>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, PostgreSQL Developers <pgsql-hackers@postgresql.org>
Date: 2017-04-03T19:30:09Z
Lists: pgsql-hackers 

> [...] but OTOH "\if sql 1 from table where expr" looks awkward. Given an 
> implicit select, I would prefer "\if exists (select 1 from table where 
> expr)" but now it's not shorter.

Possibly, but it is just an SQL expression, which looks good in the middle 
of an sql script.

> An advantage of prepending the SELECT automatically, is that it
> would prevent people from abusing this syntax by putting
> update/insert/delete or even DDL in there, imagining that this would
> be a success/failure test for these operations.

> Having these fail to execute in the first place, when called by \if,
> seems like a sane failure mode that we would gain incidentally.

Yes, it should be avoided.

-- 
Fabien.

Commits

  1. Add psql variables showing server version and psql version.

  2. Reformat psql's --help=variables output.

  3. Remove reinvention of stringify macro.

  4. Allow psql variable substitution to occur in backtick command strings.