wuchong commented on a change in pull request #9511: [FLINK-13356][table][docs]
Add documentation for TopN and Deduplication in blink planner
URL: https://github.com/apache/flink/pull/9511#discussion_r316680304
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File path: docs/dev/table/sql.md
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@@ -813,6 +813,222 @@ LIMIT 3
{% top %}
+### Top-N
+
+TopN is used to calculate the maximum/minimum N records in a stream. It can be
flexibly completed based on OVER window aggregation. The grammar is shown as
below:
+
+Top-N queries ask for the N smallest or largest values ordered by columns.
Both smallest and largest values sets are considered Top-N queries. Top-N
queries are useful in cases where the need is to display only the N bottom-most
or the N top-
+most records from batch/stream table on a condition. This result set can be
used for further analysis.
+
+Flink uses the combination of a OVER window clause and a filter condition to
express a Top-N query. With the power of OVER window `PARTITION BY` clause,
Flink also supports per group Top-N. For example, the top five products per
category that have the maximum sales in realtime. Top-N queries are supported
for SQL on batch and streaming tables.
Review comment:
I think we also support this in batch?
The attention part and optimization part is only relative to streaming. I
can explain it more detailed.
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