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Re: SQL Question

From: "Kevin Crenshaw" <kcrenshaw(at)viscient(dot)com>
To: "'Sean Davis'" <sdavis2(at)mail(dot)nih(dot)gov>,<pgsql-novice(at)postgresql(dot)org>
Subject: Re: SQL Question
Date: 2006-02-23 16:18:15
Message-ID: 20060223161819.ED4329DCA62@postgresql.org (view raw or flat)
Thread:
Lists: pgsql-novice
That did the trick.  Thanks for your help!

 

-----Original Message-----
From: pgsql-novice-owner(at)postgresql(dot)org
[mailto:pgsql-novice-owner(at)postgresql(dot)org] On Behalf Of Sean Davis
Sent: Wednesday, February 22, 2006 10:03 AM
To: Kevin Crenshaw; pgsql-novice(at)postgresql(dot)org
Subject: Re: [NOVICE] SQL Question




On 2/22/06 9:43 AM, "Kevin Crenshaw" <kcrenshaw(at)viscient(dot)com> wrote:

> I have a table called 'tasks' with a structure like this:
>  
> Taskid            ParentId
> ----------------------------
> 1                                                                    null
> 2                                                                    1
> 3                                                                    1
> 4                                                                    Null
> 5                                                                    4
> 6                                                                    4
> 7                                                                    Null
> 8                                                                    Null
> 9                                                                    15
> 10                                                                18
>  
>  
> The taskid column is the primary key and the parentid column references
> values in the taskid column.  However, it is possible for the parentid to
be
> a value that is not found in the taskid column (hence my question.).  I
need
> to write a query that will retrieve all rows where the parentid is either
> 'null' or does not exist in the taskid column.

How about:

Select * from tasks where parentid is null or parentid not in (select
distinct(taskid) from tasks);




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