List: General Discussion « Previous MessageNext Message » From: Peter Brawley Date: September 27 2006 3:20pm Subject: Re: AW: Count of children View as plain text
```André

With an edge list, the solution entails recursion, so you need either an
sproc or application proc. With a nested sets model, the count is dead
simple. If the id of the target row is N, and the left & right node
columns are named leftedge and rightedge, the query is

SELECT COUNT(t2.id)
FROM tbl t1
JOIN tbl t2 ON t2.leftedge > t1.leftedge AND t2.leftedge < t1.rightedge
WHERE t1.id=N;

PB

-----

André Hänsel wrote:
> I will use any model that is suitable. ;)
>
> I am somewhat familiar with both tree models but I can't come up with a
> method to get the count of all sub- and sub-sub-nodes in either of them.
>
>
>> -----Ursprüngliche Nachricht-----
>> Von: Peter Brawley [mailto:peter.brawley@stripped]
>> Gesendet: Mittwoch, 27. September 2006 16:49
>> An: André Hänsel
>> Cc: mysql@stripped
>> Betreff: Re: Count of children
>>
>> André,
>>
>>
>>> I want the count of all sub-entries for a specific entry.
>>>
>> Depends on the model you are using--edge list or nested sets?
>>
>> PB
>>
>> -----
>>
>> André Hänsel wrote:
>>
>>> I have a table with id and parent_id.
>>> I want the count of all sub-entries for a specific entry.
>>>
>>> I found several documents about working with graphs/trees
>>>
>> in MySQL but I
>>
>>> could not find a solution for my problem.
>>>
>>> I can imagine two possibilities, but one is memory
>>>
>> intensive and the other
>>
>>> The first is, that I select all entries and then use a
>>>
>> procedural language
>>
>>> to determine recursively whether an node is a sub-node of
>>>
>> the specific node.
>>
>>> The second is, that I store the sub-node count with each
>>>
>> node and when I do
>>
>>> an insert, I walk the tree upwards and increment the node-counts.
>>>
>>> Is there a smart solution/best practice for my problem?
>>>
>>> Now I can't think of another sentence starting with an i. ;-)
>>>
>>> Best regards,
>>> André
>>>
>>>
>>>
>>>
>> --
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>>
>>
>
>
>
>

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