Quoth mark@summersault.com (Mark Stosberg):
> On 2003-10-22, Timo <siroco@suomi24.fi> wrote:
>>
>> You can't have any recursion in an pure sql-query, can you?
>
> It depends on how you think of recursion, I'd say. You join on the same
> table a number of times, by giving it a different alias each time. You
> have to manually specify (or generate with application code) all these
> aliases and joins, though. Sometimes people use this technique to
> implement tree structures in SQL.
There is apparently an SQL 1999 feature that expressly supports
recursion.
WITH RECURSIVE Q1 AS SELECT ... FROM ... WHERE ... Q2 AS SELECT ... FROM ... WHERE ... SELECT ... FROM Q1, Q2
WHERE...
See example here...
<http://www.dbaiien.ac.at/proj/dlv/sql/.tuw>
There is presumably some work ongoing; support for WITH RECURSIVE is
on the TODO list, and has been discussed before...
http://archives.postgresql.org/pgsql-hackers/2003-05/msg00657.php
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