Re: Proposal: USING clause for DO statement

2009/11/21 Merlin Moncure <mmoncure@gmail.com>:
> On Sat, Nov 21, 2009 at 1:24 PM, Pavel Stehule <pavel.stehule@gmail.com> wrote:
>> 2009/11/21 Merlin Moncure <mmoncure@gmail.com>:
>>> On Sat, Nov 21, 2009 at 12:36 PM, Andrew Dunstan <andrew@dunslane.net> wrote:
>>>>> Perhaps part of the problem is that psql can't interpolate its variable
>>>>> into strings. Solving that might lessen the impetus for this, and have other
>>>>> uses besides.
>> I am not sure, if I understand well. Can you show some use cases, please?
>
> If I understand Andrew correctly,
>
> \set msg world
>
> DO $$
> BEGIN
>  RAISE NOTICE 'Hello, %', :msg;
> END
> $$;
>

This is base of my proposal :). But we cannot do it directly:

a) the body of DO statement is black box for psql parser,
b) psql does know nothing about used PL language - without this
knowledge cannot do correct substitution: plpgsq use ', java use "",
perl use ""

these points are reason, why I propose "external USING clause" - it
outside blackbox, it is common for all PL

Point b is solved via using a real params - not substitution.

Regards
Pavel