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Date: Thu, 21 Feb 2008 23:21:32 +0100
From: Michael Bouschen <mbo.tech@spree.de>
Organization: Tech@Spree Engineering
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To: jdo-dev@db.apache.org
Subject: Re: subquery: max & size()
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Hi Craig,

I agree the BNF would allow the query.

As I understood, the offending part is the aggregate on an expression 
ending in a size method call, correct? Then, the problem is not related 
to subqueries and we have it in JDO 2.0 already:
  select max(this.children.size()) from x.y.Node

Do we need to restrict the use of method calls inside of aggregate 
expressions to better support mapping JDOQL -> SQL?

Regards Michael


> Hi Christiaan,
>
> As I read the BNF for this filter, there's nothing to prevent it.
>
> But you are right that it might be difficult if not impossible to 
> translate this into SQL. Have you tried it with your favorite database 
> or JDO implementation?
>
> Craig
>
> On Feb 21, 2008, at 7:14 AM, Christiaan wrote:
>
>>
>> Hi,
>> a question about subqueries. With the subquery spec, should it be 
>> possible
>> to execute the following filter, which should return the nodes with the
>> maximum children?
>>
>> "children.size() == (select max(node.children.size()) from x.y.Node 
>> node)"
>>
>> I am asking this since the size() is probably translated into a 
>> count() and
>> I don't believe it is allowed to perform an aggregate on another 
>> aggregate
>> in sql.
>>
>> regards,
>> Christiaan
>> -- 
>> View this message in context: 
>> http://www.nabble.com/subquery%3A-max---size%28%29-tp15613074p15613074.html 
>>
>> Sent from the JDO - Development mailing list archive at Nabble.com.
>>
>
> Craig Russell
> Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
> 408 276-5638 mailto:Craig.Russell@sun.com
> P.S. A good JDO? O, Gasp!
>


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