Horton

Re: \if, \elseif, \else, \endif (was Re: PSQL commands: \quit_if, \quit_unless)

Daniel Verite <daniel@manitou-mail.org>

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From: "Daniel Verite" <daniel@manitou-mail.org>
To: "Tom Lane" <tgl@sss.pgh.pa.us>
Cc: "Corey Huinker" <corey.huinker@gmail.com>,"David G. Johnston" <david.g.johnston@gmail.com>,"Fabien COELHO" <coelho@cri.ensmp.fr>,"Greg Stark" <stark@mit.edu>,"Erik Rijkers" <er@xs4all.nl>,"Robert Haas" <robertmhaas@gmail.com>,"Jim Nasby" <Jim.Nasby@bluetreble.com>,"PostgreSQL" <pgsql-hackers@postgresql.org>,pgsql-hackers-owner@postgresql.org
Date: 2017-03-17T11:33:54Z
Lists: pgsql-hackers 
	Tom Lane wrote:

> OT_WHOLE_LINE is not what you want because that results in verbatim
> copying, without variable expansion or anything

But if we want to implement "\if defined :foo" in the future
isn't it just what we need?

Also we could leave open the option to accept an SQL expression
here. I expect people will need SQL as the evaluator in a lot of cases.
So far we need to do that:

  SELECT sql_expr ... AS varname \gset
  \if :varname
  ...
  \endif

Surely users will wonder right away why they can't write it like this
instead:

  \if (sql_expr)
  ...
  \endif

There's a precedent with \copy accepting a query inside parentheses,
using OT_WHOLE_LINE.


Best regards,
-- 
Daniel Vérité
PostgreSQL-powered mailer: http://www.manitou-mail.org
Twitter: @DanielVerite

Commits

  1. Support \if ... \elif ... \else ... \endif in psql scripting.

  2. Add a "void *" passthrough pointer for psqlscan.l's callback functions.