Shaoxuan Wang created FLINK-5564:
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Summary: User Defined Aggregates
Key: FLINK-5564
URL: https://issues.apache.org/jira/browse/FLINK-5564
Project: Flink
Issue Type: Improvement
Components: Table API & SQL
Reporter: Shaoxuan Wang
User-defined aggregates would be a great addition to the Table API / SQL.
The current aggregate interface is not well suited for the external users.
This issue proposes to redesign the aggregate such that we can expose an better
external UDAGG interface to the users. The detailed design proposal can be
found here:
https://docs.google.com/document/d/19JXK8jLIi8IqV9yf7hOs_Oz67yXOypY7Uh5gIOK2r-U/edit
Motivation:
1. The current aggregate interface is not very concise to the users. One needs
to know the design details of the intermediate Row buffer before implements an
Aggregate. Seven functions are needed even for a simple Count aggregate.
2. Another limitation of current aggregate function is that it can only be
applied on one single column. There are many scenarios which require the
aggregate function taking multiple columns as the inputs.
3. “Retraction” is not considered and covered in the current Aggregate.
4. It might be very good to have a local/global aggregate query plan
optimization, which is very promising to optimize UDAGG performance in some
scenarios.
Proposed Changes:
1. Implement an aggregate dataStream API
2. Update all the existing aggregates to use the new aggregate dataStream API
3. Provide a better User-Design Aggregate interface
4. Add retraction support
5. Add local/global aggregate
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