Re: Support COUNT(DISTINCT 'field') Query Yet?

Posted by Fabian Hueske-2 on
URL: http://deprecated-apache-flink-user-mailing-list-archive.369.s1.nabble.com/Support-COUNT-DISTINCT-field-Query-Yet-tp18343p18344.html

Hi Tao,

DISTINCT aggregates in group windows are not supported yet.

There's currently a discussion on the dev mailing list about this feature [1].

Since we are only a few days before the feature freeze of Flink 1.5.0, it might be included in 1.6.0, about 4-5 months from now.

As a workaround, you can implement a custom user-defined aggregation function [2] that performs distinct counts.

Cheers,

Fabian

[1] https://lists.apache.org/thread.html/4bdf66ce56ad5561461c8947203ccefa3fe2e4a1e48e29236f1bb8fc@%3Cdev.flink.apache.org%3E
[2] https://ci.apache.org/projects/flink/flink-docs-release-1.4/dev/table/udfs.html#aggregation-functions

2018-02-15 0:15 GMT+01:00 xiatao123 <[hidden email]>:

SELECT TUMBLE_START(event_timestamp, INTERVAL '1' HOUR), COUNT(DISTINCT
session), COUNT(DISTINCT user_id), SUM(duration), SUM(num_interactions) FROM
unified_events GROUP BY TUMBLE(event_timestamp, INTERVAL '1' HOUR)

I have the above statement my flink query running on Flink 1.3.2, but got
the error message Caused by: org.apache.flink.table.api.TableException:
Cannot generate a valid execution plan for the given query

Is the feature supported yet? if Yes, in which version of flink? If no, any
timeline to support it?

Thanks,
Tao



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