Re: WITH RECURSIVE clause -- all full and partial paths

On Fri, Jun 12, 2009 at 10:14:21PM +0200, Harald Fuchs wrote:
> In article <aaf543e90906120856r5219cf9cv7f13ba0d37494378@mail.gmail.com>,
> aryoo <howaryoo@gmail.com> writes:
>
> > Dear list,
> > In reference to the message below posted on the 'pgsql-hackers' list regarding
> > 'iterative' queries,
> > could anyone help me write the queries that return all full and all partial
> > paths from the root?
>
> Probably you want to use the following query:
>
>   WITH RECURSIVE subdepartment AS (
>     SELECT id, parent_department, name AS path
>     FROM department
>     WHERE name = 'A'
>   UNION ALL
>     SELECT d.id, d.parent_department, sd.path || '.' || d.name
>     FROM department d
>     JOIN subdepartment sd ON sd.id = d.parent_department
>   )
>   SELECT id, path
>   FROM subdepartment;

This is much easier as:

WITH RECURSIVE subdepartment AS (
  SELECT id, parent_department, ARRAY[name] AS "path"
  FROM department
  WHERE name = 'A'
UNION ALL
  SELECT d.id, d.parent_department, sd."path" || d.name
  FROM department d
  JOIN subdepartment sd ON (
    sd.id = d.parent_department
  AND
    d.name NOT IN(sd."path")  /* Make sure there are no cycles */
)
SELECT id, path
FROM subdepartment;

Cheers,
David.
--
David Fetter <david@fetter.org> http://fetter.org/
Phone: +1 415 235 3778  AIM: dfetter666  Yahoo!: dfetter
Skype: davidfetter      XMPP: david.fetter@gmail.com

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