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Xingcan Cui commented on FLINK-6233:
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Hi, [~Yuhong_kyo], thanks for the assignment. I'll devote myself to it.
Hi, [~fhueske], recently, I'm working on a time restricted theta-join for
{{DataStream}} in the API level. A demo can be found
[here|https://goo.gl/9WJiqT] and a corresponding design document is almost
finished.
The motivation for this job is that, I think we need a "general backend" in the
API level to support different kinds of joins (e.g., based on rowtime,
proctime) in the SQL/Table level, or it will be hard to maintain the diverse
(and dynamically generated?) codes in the future.
Currently, we have separated the (inner) join into different pieces, and only a
partial of the criteria can be supported now (that's why we need
[FLINK-7217|https://issues.apache.org/jira/browse/FLINK-7217]:)). I just wonder
if we could first provide a general purpose theta-join API, which may not be so
efficient but can get rid of most restrictions on the join condition (e.g.,
equi-keys). The API can either be public or be reserved for internal use. After
that, we can further do some optimizations for dedicated join conditions to
make the execution more efficient. What do you think?
As for the challenge you mentioned, I'm not sure if it's related to [the
question|https://lists.apache.org/thread.html/4f529715984195997441ff80922125019436fe07bc768105d26b0eb6@%3Cdev.flink.apache.org%3E]
I asked before. To keep a consistent time system for the whole stream, we are
really faced with the "time interruption" problem, e.g., how to define and
handle the timestamp of an aggregated or joined result, especially when further
processing is needed. Do I get the point?
> Support rowtime inner equi-join between two streams in the SQL API
> ------------------------------------------------------------------
>
> Key: FLINK-6233
> URL: https://issues.apache.org/jira/browse/FLINK-6233
> Project: Flink
> Issue Type: Sub-task
> Components: Table API & SQL
> Reporter: hongyuhong
> Assignee: Xingcan Cui
>
> The goal of this issue is to add support for inner equi-join on proc time
> streams to the SQL interface.
> Queries similar to the following should be supported:
> {code}
> SELECT o.rowtime , o.productId, o.orderId, s.rowtime AS shipTime
> FROM Orders AS o
> JOIN Shipments AS s
> ON o.orderId = s.orderId
> AND o.rowtime BETWEEN s.rowtime AND s.rowtime + INTERVAL '1' HOUR;
> {code}
> The following restrictions should initially apply:
> * The join hint only support inner join
> * The ON clause should include equi-join condition
> * The time-condition {{o.rowtime BETWEEN s.rowtime AND s.rowtime + INTERVAL
> '1' HOUR}} only can use rowtime that is a system attribute, the time
> condition only support bounded time range like {{o.rowtime BETWEEN s.rowtime
> - INTERVAL '1' HOUR AND s.rowtime + INTERVAL '1' HOUR}}, not support
> unbounded like {{o.rowtime < s.rowtime}} , and should include both two
> stream's rowtime attribute, {{o.rowtime between rowtime () and rowtime () +
> 1}} should also not be supported.
> An row-time streams join will not be able to handle late data, because this
> would mean in insert a row into a sorted order shift all other computations.
> This would be too expensive to maintain. Therefore, we will throw an error if
> a user tries to use an row-time stream join with late data handling.
> This issue includes:
> * Design of the DataStream operator to deal with stream join
> * Translation from Calcite's RelNode representation (LogicalJoin).
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