SQL advice needed

From: Torsten Förtsch <torsten(dot)foertsch(at)gmx(dot)net>
To: pgsql-general(at)postgresql(dot)org
Subject: SQL advice needed
Date: 2014-03-17 20:21:36
Message-ID: 53275950.9060701@gmx.net
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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.

Thanks,
Torsten

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