Hi Kurt, Thanks for your questions. Here are my thoughts.
> if I want to write such kind function, should I make sure that this function is used with some keys? The key information may not be used. We can also use RetractSink to emit the table directly. > If I need a use case to calculate topn without key, should I write another function or I can reuse previous one. For the TopN example, you can reuse the previous function if you don't care about the key information. So, the key information is only an indicator(or a description), not an operator, as Jincheng mentioned above. We do not need to change the function logic and it will not add any other aggregations. BTW, we have three approaches in the document. Approach 1 defines keys on API level as we think it's more common to define keys on Table. While approach 3 defines keys in the TableAggregateFunction which is more precise but it is not very clear for Table users. So, we should take all these into consideration, and make the decision in this discussion thread. You can take a look at the document and welcome any suggestions or other better solutions. Best, Hequn On Mon, Jul 1, 2019 at 12:13 PM Kurt Young <ykt...@gmail.com> wrote: > Hi Jincheng, > > Thanks for the clarification. Take 'TopN' for example, if I want to write > such kind function, > should I make sure that this function is used with some keys? If I need a > use case to calculate > topn without key, should I write another function or I can reuse previous > one. > > I'm not sure about the idea of this does not involve semantic changes. To > me, it sounds like > we are doing another nested aggregation inside the table > which TableAggregateFunction emits. > > Maybe I'm not familiar with this function enough, hope you can help me to > understand. > > Best, > Kurt > > > On Mon, Jul 1, 2019 at 11:59 AM jincheng sun <sunjincheng...@gmail.com> > wrote: > > > Hi Kurt, > > > > Thanks for your questions, I am glad to share my thoughts here: > > > > My question is, will that effect the logic ofTableAggregateFunction user > > > wrote? Should the user know that there will a key and make some changes > > to > > > this function? > > > > > > No, the keys information depends on the implementation of the > > TableAggregateFunction. > > For example, for a `topN` user defined TableAggregateFunction, we can > only > > use the `keys` if the `topN` contains `rankid` in the output. You can > > treat the > > `keys` like an indicator. > > > > If not, how will framework deal with the output of user's > > > TableAggregateFunction. if user output multiple rows with the same > key, > > > should be latter one replace previous ones? > > > > > > If a TableAggregateFunction outputs multiple rows with the same key, the > > latter one should replace the previous one, either with upsert mode or > > retract mode. i.e., Whether the user defines the Key or not, the Flink > > framework should ensure the correctness of the semantics. > > > > At present, the problem we are discussing does not involve semantic > > changes. The definition of keys is to support non-window flatAggregate on > > upsert mode. (The upsert mode is already supported in the flink > framework. > > The current discussion only needs to inform the framework that the keys > > information, which is the `withKeys` API we discussing.) > > > > Welcome any other feedbacks :) > > > > Best, > > Jincheng > > > > Kurt Young <ykt...@gmail.com> 于2019年7月1日周一 上午9:23写道： > > > > > Hi, > > > > > > I have a question about the key information of TableAggregateFunction. > > > IIUC, you need to define > > > something like primary key or unique key in the result table of > > > TableAggregateFunction, and also > > > need a way to let user configure this through the API. My question is, > > will > > > that effect the logic of > > > TableAggregateFunction user wrote? Should the user know that there > will a > > > key and make some changes > > > to this function? > > > > > > If so, what's the semantic the user should learned. If not, how will > > > framework deal with the output of user's > > > TableAggregateFunction. For example, if user output multiple rows with > > the > > > same key, should be latter one > > > replace previous ones? > > > > > > Best, > > > Kurt > > > > > > > > > On Mon, Jul 1, 2019 at 7:19 AM jincheng sun <sunjincheng...@gmail.com> > > > wrote: > > > > > > > Hi hequn, Thanks for the reply! I think `withKeys` solution is our > > better > > > > choice! > > > > > > > > > > > > Hequn Cheng <chenghe...@gmail.com> 于2019年6月26日周三 下午5:11写道： > > > > > > > > > Hi Jincheng, > > > > > > > > > > Thanks for raising the discussion! > > > > > The key information is very important for query optimizations. It > > would > > > > be > > > > > nice if we can use upsert mode to achieve better performance. > > > > > > > > > > +1 for the `withKeys` proposal. :) > > > > > > > > > > Best, Hequn > > > > > > > > > > > > > > > On Wed, Jun 26, 2019 at 4:37 PM jincheng sun < > > sunjincheng...@gmail.com > > > > > > > > > wrote: > > > > > > > > > > > Hi all, > > > > > > > > > > > > With the continuous efforts from the community, we already > > supported > > > > > > `flatAggregate`[1] on TableAPI in retract mode. I think It's > better > > > to > > > > > add > > > > > > upsert mode for `flatAggregate`. > > > > > > > > > > > > The result table of streaming non-window `flatAggregate` is a > table > > > > > > contains updates. We can, of course, use a > > RetractStreamTableSink[2] > > > to > > > > > > emit the table, but we can get better performance in upsert mode. > > > > > However, > > > > > > due to the lack of keys, we can’t use an UpsertStreamTableSink to > > > emit > > > > > the > > > > > > table. We don’t have this problem for a normal aggregate as it > > emits > > > a > > > > > > single row for each group, so the unique keys are exactly the > same > > > with > > > > > the > > > > > > group keys. While for a `flatAggregate`, its pretty difference > that > > > due > > > > > to > > > > > > emits multi rows(a “sub-table”) for a single group. To solve this > > > > > problem, > > > > > > we need to find a way to define keys on flatAggregate, so that we > > can > > > > > also > > > > > > use upsert sink to emit the result table after flatAggregate. > > > > > > > > > > > > So, Aljoscha, Hequn and I prepared a design document for how to > > > define > > > > > the > > > > > > update keys for `flatAggregate` in upsert mode. The detail can > be > > > > found > > > > > > here: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://docs.google.com/document/d/183qHo8PDG-xserDi_AbGP6YX9aPY0rVr80p3O3Gyz6U/edit?usp=sharing > > > > > > > > > > > > I appreciate it if you can have look at the document and any > > comments > > > > are > > > > > > welcome! > > > > > > > > > > > > > > > > > > Best, > > > > > > > > > > > > Jincheng > > > > > > > > > > > > > > > > > > [1] > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=97552739 > > > > > > > > > > > > [2] > > > > > > > > > > > > > > > > > > > > > > > > > > > https://ci.apache.org/projects/flink/flink-docs-release-1.8/dev/table/sourceSinks.html#defining-a-streamtablesource > > > > > > > > > > > > > > > > > > > > >
