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https://issues.apache.org/jira/browse/FLINK-7599?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16708923#comment-16708923
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ASF GitHub Bot commented on FLINK-7599:
---------------------------------------
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_r238709945
##########
File path:
flink-libraries/flink-table/src/main/scala/org/apache/flink/table/codegen/MatchCodeGenerator.scala
##########
@@ -49,6 +50,90 @@ import scala.collection.mutable
/**
* A code generator for generating CEP related functions.
*
+ * Aggregates are generated as follows:
+ * 1. all aggregate [[RexCall]]s are grouped by corresponding pattern variable
+ * 2. even if the same aggregation is used multiple times in an expression
+ * (e.g. SUM(A.price) > SUM(A.price) + 1) it will be calculated once. To
do so [[AggBuilder]]
+ * keeps set of already seen different aggregation calls, and reuses the
code to access
+ * appropriate field of aggregation result
+ * 3. after translating every expression (either in [[generateCondition]] or
in
+ * [[generateOneRowPerMatchExpression]]) there will be generated code for
+ * * [[GeneratedFunction]], which will be an inner class
+ * * said [[GeneratedFunction]] will be instantiated in the ctor and
opened/closed
+ * in corresponding methods of top level generated classes
+ * * function that transforms input rows (row by row) into aggregate
input rows
+ * * function that calculates aggregates for variable, that uses the
previous method
+ * The generated code will look similar to this:
+ *
+ *
+ * {{{
+ *
+ * public class MatchRecognizePatternSelectFunction$175 extends
RichPatternSelectFunction {
+ *
+ * // Class used to calculate aggregates for a single pattern variable
+ * public final class AggFunction_variable$115$151 extends
GeneratedAggregations {
+ * ...
+ * }
+ *
+ * private final AggFunction_variable$115$151 aggregator_variable$115;
+ *
+ * public MatchRecognizePatternSelectFunction$175() {
+ * aggregator_variable$115 = new AggFunction_variable$115$151();
+ * }
+ *
+ * public void open() {
+ * aggregator_variable$115.open();
+ * ...
+ * }
+ *
+ * // Function to transform incoming row into aggregate specific row. It
can e.g calculate
+ * // inner expression of said aggregate
+ * private Row transformRowForAgg_variable$115(Row inAgg) {
+ * ...
+ * }
+ *
+ * // Function to calculate all aggregates for a single pattern variable
+ * private Row calculateAgg_variable$115(List<Row> input) {
+ * Acc accumulator = aggregator_variable$115.createAccumulator();
+ * for (Row row : input) {
+ * aggregator_variable$115.accumulate(accumulator,
transformRowForAgg_variable$115(row));
+ * }
+ *
+ * return aggregator_variable$115.getResult(accumulator);
+ * }
+ *
+ * @Override
+ * public Object select(Map<String, List<Row>> in1) throws Exception {
+ *
+ * // Extract list of rows assigned to a single pattern variable
+ * java.util.List patternEvents$130 = (java.util.List) in1.get("A");
+ * ...
+ *
+ * // Calculate aggregates
+ * Row aggRow_variable$110$111 =
calculateAgg_variable$110(patternEvents$114);
+ *
+ * // Every aggregation (e.g SUM(A.price) and AVG(A.price)) will be
extracted to a variable
+ * double result$135 = aggRow_variable$126$127.getField(0);
+ * long result$137 = aggRow_variable$126$127.getField(1);
+ *
+ * // Result of aggregation will be used in expression evaluation
+ * out.setField(0, result$135)
+ *
+ * long result$140 = result$137 * 2;
+ * out.setField(1, result$140);
+ *
+ * double result$144 = $result135 + result$137;
+ * out.setField(2, result$144);
+ * }
+ *
+ * public void close() {
+ * aggregator_variable$115.close();
+ * ...
+ * }
+ *
+ * }
+ * }}}
+ *
Review comment:
Awesome documentation. Very helpful.
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> Support aggregation functions in the define and measures clause of
> MatchRecognize
> ---------------------------------------------------------------------------------
>
> Key: FLINK-7599
> URL: https://issues.apache.org/jira/browse/FLINK-7599
> Project: Flink
> Issue Type: Sub-task
> Components: CEP, Table API & SQL
> Reporter: Dian Fu
> Assignee: Dawid Wysakowicz
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.8.0
>
>
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