[GitHub] [druid] suneet-s commented on a change in pull request #8719: GREATEST/LEAST post-aggregators in SQL

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suneet-s commented on a change in pull request #8719: GREATEST/LEAST post-aggregators in SQL
URL: https://github.com/apache/druid/pull/8719#discussion_r373879235
 
 

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 File path: sql/src/main/java/org/apache/druid/sql/calcite/aggregation/builtin/GreatestSqlAggregator.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.sql.calcite.aggregation.builtin;
+
+import org.apache.calcite.sql.SqlAggFunction;
+import org.apache.calcite.sql.SqlFunctionCategory;
+import org.apache.calcite.sql.SqlKind;
+import org.apache.calcite.sql.type.OperandTypes;
+import org.apache.calcite.sql.type.ReturnTypes;
+import org.apache.druid.java.util.common.ISE;
+import org.apache.druid.math.expr.ExprMacroTable;
+import org.apache.druid.query.aggregation.AggregatorFactory;
+import org.apache.druid.query.aggregation.DoubleMaxAggregatorFactory;
+import org.apache.druid.query.aggregation.LongMaxAggregatorFactory;
+import org.apache.druid.query.aggregation.PostAggregator;
+import org.apache.druid.query.aggregation.post.DoubleGreatestPostAggregator;
+import org.apache.druid.query.aggregation.post.LongGreatestPostAggregator;
+import org.apache.druid.segment.column.ValueType;
+
+import java.util.List;
+
+/**
+ * Calcite integration class for Greatest post aggregators of Long & Double types.
+ * It applies Max aggregators over the provided fields/expressions & combines their results via Field access post aggregators.
+ */
+public class GreatestSqlAggregator extends MultiColumnSqlAggregator
+{
+  private static final SqlAggFunction FUNCTION_INSTANCE = new GreatestSqlAggFunction();
+  private static final String NAME = "GREATEST";
+
+  @Override
+  public SqlAggFunction calciteFunction()
+  {
+    return FUNCTION_INSTANCE;
+  }
+
+  @Override
+  AggregatorFactory createAggregatorFactory(
+      ValueType valueType,
+      String prefixedName,
+      FieldInfo fieldInfo,
+      ExprMacroTable macroTable
+  )
+  {
+    final AggregatorFactory aggregatorFactory;
+    switch (valueType) {
+      case LONG:
+        aggregatorFactory = new LongMaxAggregatorFactory(prefixedName, fieldInfo.fieldName, fieldInfo.expression, macroTable);
+        break;
+      case FLOAT:
+      case DOUBLE:
+        aggregatorFactory = new DoubleMaxAggregatorFactory(prefixedName, fieldInfo.fieldName, fieldInfo.expression, macroTable);
+        break;
+      default:
+        throw new ISE("Cannot create aggregator factory for type[%s]", valueType);
 
 Review comment:
   Add a unit test for this function that fails when someone adds a new `ValueType`. This way we can catch cases where someone adds a new type that should have support in the Greatest aggregator.
   
   It would also be good to add tests that validate the expected aggregator factories are returned for the types LONG, FLOAT and DOUBLE

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