[beam] branch master updated: [BEAM-10925] Add SQL AggregateFn interface.

[ib...@apache.org]

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ibzib pushed a commit to branch master
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The following commit(s) were added to refs/heads/master by this push:
     new 3de4f88  [BEAM-10925] Add SQL AggregateFn interface.
     new a7457c0  Merge pull request #13306 from ibzib/aggregate-udf
3de4f88 is described below

commit 3de4f88aa8839af36e355060c8de62f9a6caf0e7
Author: Kyle Weaver <kc...@google.com>
AuthorDate: Wed Nov 11 13:05:20 2020 -0800

    [BEAM-10925] Add SQL AggregateFn interface.
---
 .../beam/sdk/extensions/sql/udf/AggregateFn.java   | 70 ++++++++++++++++++++++
 1 file changed, 70 insertions(+)

diff --git a/sdks/java/extensions/sql/udf/src/main/java/org/apache/beam/sdk/extensions/sql/udf/AggregateFn.java b/sdks/java/extensions/sql/udf/src/main/java/org/apache/beam/sdk/extensions/sql/udf/AggregateFn.java
new file mode 100644
index 0000000..28ebf3b
--- /dev/null
+++ b/sdks/java/extensions/sql/udf/src/main/java/org/apache/beam/sdk/extensions/sql/udf/AggregateFn.java
@@ -0,0 +1,70 @@
+/*
+ * 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.beam.sdk.extensions.sql.udf;
+
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+/**
+ * An aggregate function that can be executed as part of a SQL query.
+ *
+ * <p>AggregateFn contains a subset of the functionality of {@code
+ * org.apache.beam.sdk.transforms.Combine.CombineFn}.
+ *
+ * <p>AggregateFn is <strong>experimental</strong>. Compatibility is not guaranteed across Beam
+ * versions.
+ *
+ * @param <InputT> type of input values
+ * @param <AccumT> type of mutable accumulator values
+ * @param <OutputT> type of output values
+ */
+public interface AggregateFn<
+    InputT extends @Nullable Object,
+    AccumT extends @Nullable Object,
+    OutputT extends @Nullable Object> {
+
+  /**
+   * Returns a new, mutable accumulator value, representing the accumulation of zero input values.
+   */
+  AccumT createAccumulator();
+
+  /**
+   * Adds the given input value to the given accumulator, returning the new accumulator value.
+   *
+   * @param mutableAccumulator may be modified and returned for efficiency
+   * @param input should not be mutated
+   */
+  AccumT addInput(AccumT mutableAccumulator, InputT input);
+
+  /**
+   * Returns an accumulator representing the accumulation of all the input values accumulated in the
+   * merging accumulators.
+   *
+   * @param accumulators only the first accumulator may be modified and returned for efficiency; the
+   *     other accumulators should not be mutated, because they may be shared with other code and
+   *     mutating them could lead to incorrect results or data corruption.
+   */
+  AccumT mergeAccumulators(Iterable<AccumT> accumulators);
+
+  /**
+   * Returns the output value that is the result of combining all the input values represented by
+   * the given accumulator.
+   *
+   * @param accumulator can be modified for efficiency
+   */
+  OutputT extractOutput(AccumT accumulator);
+}