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From Riyafa Abdul Hameed <riyafa...@cse.mrt.ac.lk>
Subject Re: Creating aggregate functions
Date Sun, 23 Jul 2017 04:43:05 GMT
Hi,

Thanks for the explanation.
But there are so many things I still don't understand. One of them is for
the avg function itself there are several FuntionIdentifiers. What do they
all mean?

I see AVG, LOCAL_AVG, INTERMEDIATE_AVG and GLOBAL_AVG.

What do they all mean?
Please help

On 19 July 2017 at 21:56, Yingyi Bu <buyingyi@gmail.com> wrote:

> Hi Riyafa,
>
>    >> ScalarCountAggregateDescriptor
>   It's used for counting a scalar array that appears inside a tuple.
>   For example:
>   SELECT u.id, array_count(u.friends)
>   FROM users u;
>
>    >> SerializableCountAggregateDescriptor
>    Serialized aggregation descriptor implementations are only used in
> hash-based group-by.
>    For example:
>    SELECT u.city, count(*)
>    FROM users u
>    /*+ hash */
>    GROUP BY u.city;
>
>   If your aggregation function doesn't have a fixed-byte-sized state, you
> don't need to worry about that or implement that.
>
>    >> CountAggregateDescriptor
>    This is used in group-by or global aggregate:
>    For example:
>    SELECT u.city, count(*)
>    FROM users u
>    GROUP BY u.city;
>
>    SELECT count(*) FROM users;
>
>
> Best,
> Yingyi
>
>
> On Wed, Jul 19, 2017 at 7:55 AM, Riyafa Abdul Hameed <riyafa@apache.org>
> wrote:
>
> > Hi again,
> >
> > Any suggestions on this? Or anyone I can reach to who are not on this
> list
> > or not active on the list?
> >
> > Thank you.
> >
> > On 17 July 2017 at 17:18, Riyafa Abdul Hameed <riyafa@apache.org> wrote:
> >
> > > Hi again,
> > >
> > > I think I can understand how to write the descriptor in the packages:
> > > org.apache.asterix.runtime.aggregates.std and
> > org.apache.asterix.runtime.aggregates.scalar.
> > > But I am not sure I understand how to write the descriptor in the
> > package:
> > > org.apache.asterix.runtime.aggregates.serializable.std  because it
> > > requires setting a state in the init function that doesn't seem to
> have a
> > > pattern in the other descriptors.
> > > Also I don't seem to understand the reasons for implementing each of
> > these
> > > descriptors for the aggregate functions.
> > >
> > > On 17 July 2017 at 16:56, Riyafa Abdul Hameed <riyafa.12@cse.mrt.ac.lk
> >
> > > wrote:
> > >
> > >> Hi all,
> > >>
> > >> I meant any explanation on the implementation of aggregate functions
> in
> > >> AsterixDB would be highly appreciated.
> > >>
> > >> Thank you.
> > >> Yours sincerely,
> > >> Riyafa
> > >>
> > >> On 16 July 2017 at 08:01, Riyafa Abdul Hameed <riyafa@apache.org>
> > wrote:
> > >>
> > >>> Dear all,
> > >>>
> > >>> I am trying to create aggregate functions and I see there are more
> than
> > >>> one function descriptors for one single function.
> > >>> For example the function array_count(collection) has the following
> > >>> descriptors:
> > >>>
> > >>>
> > >>>    - ScalarCountAggregateDescriptor
> > >>>    - SerializableCountAggregateDescriptor
> > >>>    - CountAggregateDescriptor
> > >>>
> > >>> I am not sure I understand the difference between each of this. Can
> you
> > >>> please provide and example or point me to a documentation entry to
> > learn
> > >>> how to properly implement aggregate functions?
> > >>>
> > >>> The function I am trying to implement is ST_Extent.
> > >>> <https://postgis.net/docs/manual-1.4/ST_Extent.html>
> > >>>
> > >>> Thank you.
> > >>>
> > >>> Yours sincerely,
> > >>>
> > >>> Riyafa
> > >>>
> > >>
> > >>
> > >>
> > >> --
> > >> Riyafa Abdul Hameed
> > >> Undergraduate, University of Moratuwa
> > >>
> > >> Email: riyafa.12@cse.mrt.ac.lk
> > >> Website: https://riyafa.wordpress.com/ <http://riyafa.wordpress.com/>
> > >> <http://facebook.com/riyafa.ahf>  <http://lk.linkedin.com/in/riyafa>
> > >> <http://twitter.com/Riyafa1>
> > >>
> > >
> > >
> >
>



-- 
Riyafa Abdul Hameed
Undergraduate, University of Moratuwa

Email: riyafa.12@cse.mrt.ac.lk
Website: https://riyafa.wordpress.com/ <http://riyafa.wordpress.com/>
<http://facebook.com/riyafa.ahf>  <http://lk.linkedin.com/in/riyafa>
<http://twitter.com/Riyafa1>

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