Re: Having a mental block with (self) outer joins

On Mon, Apr 21, 2008 at 03:48:23PM +0200, Thomas Kellerer wrote:
> name, id, parent_id
> ROOT, 1, NULL
> CHILD1, 2, 1
> CHILD2, 3, 1
>
> I would have expected the following result:
>
> ROOT, NULL
> ROOT, CHILD1
> ROOT, CHILD2
>
> but the row with (ROOT,NULL) is not returned.

why would you expect it?
the columns are: parent and child (on your output).
you dont have any row that has *parent_id = 1* and id = NULL.

you can get this output though:

NULL, ROOT
ROOT, CHILD1
ROOT, CHILD2

with this query:

select p.name as parent, c.name as child from category c left outer join category p on c.parent_id = p.id

depesz

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