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From "Xingcan Cui (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-6233) Support rowtime inner equi-join between two streams in the SQL API
Date Thu, 20 Jul 2017 12:51:02 GMT

    [ https://issues.apache.org/jira/browse/FLINK-6233?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16094634#comment-16094634
] 

Xingcan Cui commented on FLINK-6233:
------------------------------------

Hi [~fhueske],

thanks for sharing. I totally agree to your first two ideas on the timestamp. Regarding to
the last one on watermark, I have some questions.
# What happens if we just provide the needed timestamps and do nothing to the original watermarks?
Some results triggered by the watermarks (which means they are generated AFTER the corresponding
watermarks) would be treated as delayed and thus may not be correctly processed by the downstream
functions, right?
# When said "holding back", did you mean the original/old watermarks should be swallowed by
some special operators so that the downstream components will never receive them?
# If the downstream operators are time-based, users have to assign new timestamp fields from
the projected fields and thus new watermarks should also be automatically generated and propagated,
right? 
# If the timestamp field can be reassigned, is it necessary to restrict that the new field
must be one of the old timestamp fields (from the left or right streams), so that the old
watermarks may be reused somehow?

Thanks, Xingcan

> 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 &lt; 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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