twalthr commented on a change in pull request #7177: [FLINK-7599] [table]
Support for aggregates in MATCH_RECOGNIZE
URL: https://github.com/apache/flink/pull/7177#discussion_r241787811
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File path: docs/dev/table/streaming/match_recognize.md
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@@ -211,6 +211,65 @@ If a condition is not defined for a pattern variable, a
default condition will b
For a more detailed explanation about expressions that can be used in those
clauses, please have a look at the [event stream
navigation](#pattern-navigation) section.
+### Aggregations
+
+Aggregations can be used in `DEFINE` and `MEASURES` clauses. Both
[built-in]({{ site.baseurl }}/dev/table/sql.html#built-in-functions) and custom
[user defined]({{ site.baseurl }}/dev/table/udfs.html) functions are supported.
+
+Aggregate functions are applied to each subset of rows mapped to a match. In
order to understand how those subsets are evaluated have a look at the [event
stream navigation](#pattern-navigation) section.
+
+The task of the following example is to find the longest period of time for
which the average price of a ticker did not go below certain threshold. It
shows how expressible `MATCH_RECOGNIZE` can become with aggregations.
+This task can be performed with the following query:
+
+{% highlight sql %}
+SELECT *
+FROM Ticker
+MATCH_RECOGNIZE (
+ PARTITION BY symbol
+ ORDER BY rowtime
+ MEASURES
+ FIRST(A.rowtime) AS start_tstamp,
+ LAST(A.rowtime) AS end_tstamp,
+ AVG(A.price) AS avgPrice
+ ONE ROW PER MATCH
+ AFTER MATCH SKIP TO FIRST B
+ PATTERN (A+ B)
+ DEFINE
+ A AS AVG(A.price) < 15
+ ) MR;
Review comment:
@dawidwys what is `MR` actually doing? Do we have to call `SELECT
MR.start_tstamp`?
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