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From: Pavel Stehule on 16 Dec 2009 10:42
2009/12/16 Thom Brown <thombrown(a)gmail.com>:
> 2009/12/15 Pavel Stehule <pavel.stehule(a)gmail.com>
>>
>> Hello
>>
>> I am looking on new feature - ORDER clause in aggregate, and I thing,
>> so we are able to effectively implement some non standard, but well
>> known aggregates.
>>
>> a) function median - it is relative frequent request - with usually
>> slow implementation
>>
>> b) function listagg (it is analogy of group_concat from MySQL) - it
>> should simplify report generating and some other
>>
>> What is your opinion? Do you like to see these functions in core?
>>
>>
>
> I'm probably missing the point here, but when I originally saw MySQL's
> group_concat function, I found it odd that it featured ordering
> functionality.  Shouldn't the order by determined by the query itself?
> Otherwise it's almost as if its separating the relationship between the
> result column and the resultset.
>

Aggregates as group_concat or listagg are not typical SQL aggregates.
With these aggregates we are able to do some reports on SQL level
without stored procedures. What I know, order is determined only for
non hash aggregates - and you cannot specify method of aggregation, so
possibility to specify ORDER is important. But this feature isn't
related to this "proposal". It was commited yesterday - so you can
look on discussion about this feature.

Regards
Pavel Stehuke

> Thom
>
>

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From: Scott Bailey on 16 Dec 2009 11:10
Thom Brown wrote:
> 2009/12/15 Pavel Stehule <pavel.stehule(a)gmail.com
> <mailto:pavel.stehule(a)gmail.com>>
>
> Hello
>
> I am looking on new feature - ORDER clause in aggregate, and I thing,
> so we are able to effectively implement some non standard, but well
> known aggregates.
>
> a) function median - it is relative frequent request - with usually
> slow implementation
>
> b) function listagg (it is analogy of group_concat from MySQL) - it
> should simplify report generating and some other
>
> What is your opinion? Do you like to see these functions in core?
>
>
>
> I'm probably missing the point here, but when I originally saw MySQL's
> group_concat function, I found it odd that it featured ordering
> functionality. Shouldn't the order by determined by the query itself?
> Otherwise it's almost as if its separating the relationship between the
> result column and the resultset.

For xmlagg in particular, it is quite useful to be able order the
results. And sorting the query doesn't work for ordering the agg unless
you do it in a subquery. Oracle has this functionality and it is quite
handy. It would be nice to see listagg with the option to order as well.

Scott

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