[GitHub] [druid] jon-wei commented on a change in pull request #9183: fix topn aggregation on numeric columns with null values

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jon-wei commented on a change in pull request #9183: fix topn aggregation on numeric columns with null values
URL: https://github.com/apache/druid/pull/9183#discussion_r367748677
 
 

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 File path: processing/src/main/java/org/apache/druid/query/topn/types/NullableNumericTopNColumnAggregatesProcessor.java
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+/*
+ * 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.druid.query.topn.types;
+
+import org.apache.druid.common.config.NullHandling;
+import org.apache.druid.query.aggregation.Aggregator;
+import org.apache.druid.query.topn.BaseTopNAlgorithm;
+import org.apache.druid.query.topn.TopNParams;
+import org.apache.druid.query.topn.TopNQuery;
+import org.apache.druid.query.topn.TopNResultBuilder;
+import org.apache.druid.segment.BaseNullableColumnValueSelector;
+import org.apache.druid.segment.Cursor;
+import org.apache.druid.segment.StorageAdapter;
+
+import java.util.Map;
+import java.util.function.Function;
+
+public abstract class NullableNumericTopNColumnAggregatesProcessor<Selector extends BaseNullableColumnValueSelector>
+    implements TopNColumnAggregatesProcessor<Selector>
+{
+  private final boolean hasNulls = !NullHandling.replaceWithDefault();
+  final Function<Object, Comparable<?>> converter;
+  Aggregator[] nullValueAggregates;
+
+  protected NullableNumericTopNColumnAggregatesProcessor(Function<Object, Comparable<?>> converter)
+  {
+    this.converter = converter;
+  }
+
+  abstract Aggregator[] getValueAggregators(TopNQuery query, Selector selector, Cursor cursor);
+
+  abstract Map<?, Aggregator[]> getAggregatesStore();
+
+  abstract Comparable<?> convertAggregatorStoreKeyToColumnValue(Object aggregatorStoreKey);
+
+  @Override
+  public int getCardinality(Selector selector)
+  {
+    return TopNParams.CARDINALITY_UNKNOWN;
+  }
+
+  @Override
+  public Aggregator[][] getRowSelector(TopNQuery query, TopNParams params, StorageAdapter storageAdapter)
+  {
+    return null;
+  }
+
+  @Override
+  public long scanAndAggregate(
+      TopNQuery query,
+      Selector selector,
+      Cursor cursor,
+      Aggregator[][] rowSelector
+  )
+  {
+    initAggregateStore();
 
 Review comment:
   I think the `initAggregateStore` call could be moved into `HeapBasedTopNAlgorithm.scanAndAggregate` since both impls call it as the first step

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