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https://issues.apache.org/jira/browse/FLINK-4691?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15568789#comment-15568789
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ASF GitHub Bot commented on FLINK-4691:
---------------------------------------
Github user twalthr commented on a diff in the pull request:
https://github.com/apache/flink/pull/2562#discussion_r83009444
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/api/table/runtime/aggregate/PropertyRead.scala
---
@@ -0,0 +1,33 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.api.table.runtime.aggregate
+
+import org.apache.flink.streaming.api.windowing.windows.Window
+
+/**
+ * Base class for reading a window property. The property will be
extracted once and
+ * can be read multiple times.
+ */
+trait PropertyRead[T] extends Serializable {
+
+ def extract(window: Window): Unit
--- End diff --
Yes, every aggregation should only happen once. We should definitely do
that. Btw. we can also get rid of `AvgAggregate` once
`AggregateReduceFunctionsRule` is enabled. So there are many open issues with
the current aggregate implementation.
> Add group-windows for streaming tables
> ---------------------------------------
>
> Key: FLINK-4691
> URL: https://issues.apache.org/jira/browse/FLINK-4691
> Project: Flink
> Issue Type: Sub-task
> Components: Table API & SQL
> Reporter: Timo Walther
> Assignee: Timo Walther
>
> Add Tumble, Slide, Session group-windows for streaming tables as described in
> [FLIP-11|https://cwiki.apache.org/confluence/display/FLINK/FLIP-11%3A+Table+API+Stream+Aggregations].
>
> Implementation of group-windows on streaming tables. This includes
> implementing the API of group-windows, the logical validation for
> group-windows, and the definition of the “rowtime” and “systemtime” keywords.
> Group-windows on batch tables won’t be initially supported and will throw an
> exception.
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