Re: SQL advice needed

On Mon, Mar 17, 2014 at 3:21 PM, Torsten Förtsch
<torsten.foertsch@gmx.net> wrote:
> Hi,
>
> I have a volatile function that returns multiple rows. It may also
> return nothing. Now, I want to write an SQL statement that calls this
> function until it returns an empty result set and returns all the rows.
>
> So, in principle I want to:
>
> WITH RECURSIVE
> t AS (
>   SELECT * FROM xx()
>   UNION ALL
>   SELECT * FROM xx()
> )
> SELECT * FROM t;
>
> But that's not recursive because the union all part lacks a reference to t.
>
> Next I tried this:
>
> WITH RECURSIVE
> t AS (
>   SELECT * FROM xx()
>   UNION ALL
>   SELECT * FROM xx() WHERE EXISTS (SELECT 1 FROM t)
> )
> SELECT * FROM t;
>
> But the reference to t is not allowed in a subquery.
>
> What's the best (or at least a working) way to achieve what I want?
>
> I can do it in plpgsql. But that would mean to accumulate the complete
> result in memory first, right? I need to avoid that.

I would test that assumption.   This is better handled in loop IMO.

LOOP
  RETURN QUERY SELECT * FROM xx();
  IF NOT found
  THEN
    RETURN;
  END IF;
END LOOP;

merlin