Jark Wu created FLINK-11943:
-------------------------------
Summary: Support TopN feature for Flink SQL
Key: FLINK-11943
URL: https://issues.apache.org/jira/browse/FLINK-11943
Project: Flink
Issue Type: New Feature
Components: API / Table SQL
Reporter: Jark Wu
TopN is a frequently used feature in data analysis. We can use ORDER BY + LIMIT
to easily express a TopN query, e.g. {{SELECT * FROM T ORDER BY amount DESC
LIMIT 10}}.
But this is a global TopN, there is a great requirement for per-group TopN. For
example, top 10 shops for each category. In order to avoid introducing new
syntax for this, we would like to use traditional syntax to express it by using
{{ROW_NUMBER}} over window + {{FILTER}} to limit the numbers.
For example:
{{code}}
SELECT *
FROM (
SELECT category, shopId, sales,
[ROW_NUMBER()|RANK()|DENSE_RANK()] OVER
(PARTITION BY category ORDER BY sales ASC) as rownum
FROM shop_sales
)
WHERE rownum <= 10
{{code}}
This issue is aiming to optimize this query to an {{Rank}} node instead of
{{Over}} plus {{Calc}}. And translate the {{Rank}} node into physical operators.
There are some optimization for rank operator based on the different input of
the Rank. We would like to implement the basic and one-fit-all implementation.
And do the performance improvement later.
Here is a brief design doc:
https://docs.google.com/document/d/14JCV6X6hcpoA51loprgntZNxQ2NmnDLucxgGY8xVDuI/edit#
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