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Data Bases > Pgsql Sql > Re: Having a me...
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Re: Having a mental block with (self) outer joins

by spam_eater@[EMAIL PROTECTED] (Thomas Kellerer) Apr 21, 2008 at 04:15 PM

hubert depesz lubaczewski, 21.04.2008 16:05:
>> 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.

Ah, of course that's where my mental block was ;)
Thanks for the quick response

> 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

If the table contains more levels (i.e. child1 being the parent of another
item) this bring others back as well. And I was trying to retrieve the full
path for each item (I do know the max. number of levels)

Cheers, and thanks a lot for the quick response
Thomas


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 4 Posts in Topic:
Having a mental block with (self) outer joins
spam_eater@[EMAIL PROTECT  2008-04-21 15:48:23 
Re: Having a mental block with (self) outer joins
depesz@[EMAIL PROTECTED]   2008-04-21 16:05:21 
Re: Having a mental block with (self) outer joins
spam_eater@[EMAIL PROTECT  2008-04-21 16:15:20 
Re: Having a mental block with (self) outer joins
Dennis Muhlestein <djm  2008-04-24 16:20:57 

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