Thread: Easier string concat in PL funcs?

After for the umpteenth time bashing my head against a wall developing
some PL funcs that use dynamic SQL, going plain bonkers trying to
build the query string; I came up with a function like the one below
to take a string with placeholders, an array of values to be
interpolated and a placeholder char.  (This may appear Pythonish to
some.

Question: Am I overlooking a simple way of doing this?

As in; raise notice 'Foo % %', v_var1, v_var2;


create function make_string(v_template text, v_vars text[], v_placeholder char)
returns text
as $$

declare
    v_temp text[] := string_to_array(v_template, v_placeholder);
    v_output text[];

begin
    if array_upper(v_vars, 1) + 1 != array_upper(v_temp, 1) then
        raise exception 'Too many vars; should be equal to placeholders "%" in string', v_placeholder;
    end if;

    for i in 2 .. array_upper(v_temp, 1) * 2 by 2 loop
        v_output [i - 1] := v_temp[i / 2];
        v_output [i] := v_vars[i / 2];
    end loop;

    return array_to_string(v_output, '');

end

$$
language plpgsql;


The above function makes possible to do something like this shown
below wich for complex dynamic SQL strings, can be a lot easier to
create than with the usual combo of string constants pasted together
with PL vars using ||.

execute make_string($$
    create table fooschema.%
    ;
    create rule %
    as on insert  to fooschema.%
    where %
    do whatever
    ;
$$,
array [
    v_tablename,
    v_rulename,
    v_tablename,
    v_conditions
],
'%'
);
--
...Still not exactly simple, I realize :-)

Thanks

-------------------------------------------------------------------------------
Jerry Sievers   732 365-2844 (work)     Production Database Administrator
                305 321-1144 (mobil    WWW E-Commerce Consultant

Jerry Sievers wrote:
> After for the umpteenth time bashing my head against a wall developing
> some PL funcs that use dynamic SQL, going plain bonkers trying to
> build the query string; I came up with a function like the one below
> to take a string with placeholders, an array of values to be
> interpolated and a placeholder char.  (This may appear Pythonish to
> some.
>
> Question: Am I overlooking a simple way of doing this?
>
> As in; raise notice 'Foo % %', v_var1, v_var2;

No, you aren't.  AFAICT there isn't any way to do that, and I missed it
not too long ago.

I'm not sure about the exact syntax, and certainly I expect this to
become less of an issue with plan invalidation on 8.3, but IMHO it would
be good to have something like Python %(f)s string interpolation (or
just plain string interpolation like in other languages).

--
Alvaro Herrera                        http://www.advogato.org/person/alvherre
"Cuando no hay humildad las personas se degradan" (A. Christie)

On Wed, Oct 03, 2007 at 11:47:26AM -0400, Jerry Sievers wrote:
> Question: Am I overlooking a simple way of doing this?

yes. use plpython or plperl to do the job.

depesz

--
quicksil1er: "postgres is excellent, but like any DB it requires a
highly paid DBA.  here's my CV!" :)
http://www.depesz.com/ - blog dla ciebie (i moje CV)

On 10/3/07, hubert depesz lubaczewski <depesz@depesz.com> wrote:
> On Wed, Oct 03, 2007 at 11:47:26AM -0400, Jerry Sievers wrote:
> > Question: Am I overlooking a simple way of doing this?
>
> yes. use plpython or plperl to do the job.
>
> depesz
>


here is a great example with pl/perl  (search: printf)
http://people.planetpostgresql.org/greg/index.php?/categories/12-PlPerl

-- Parse a pipe-delimeted string:
SELECT sprintf('Total grams: %3.3f Donuts: %s',
  '101.319472|chocolate and boston cream', '|');

                         sprintf
---------------------------------------------------------
 Total grams: 101.319 Donuts: chocolate and boston cream

merlin