[GitHub] hvanhovell commented on a change in pull request #23388: [SPARK-26448][SQL] retain the difference between 0.0 and -0.0

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hvanhovell commented on a change in pull request #23388: [SPARK-26448][SQL] retain the difference between 0.0 and -0.0
URL: https://github.com/apache/spark/pull/23388#discussion_r244419215
 
 

 ##########
 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/NormalizeFloatingNumbers.scala
 ##########
 @@ -0,0 +1,179 @@
+/*
+ * 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.spark.sql.catalyst.optimizer
+
+import org.apache.spark.sql.catalyst.expressions.{Alias, And, ArrayTransform, CreateArray, CreateMap, CreateNamedStruct, CreateNamedStructUnsafe, CreateStruct, EqualTo, ExpectsInputTypes, Expression, GetStructField, LambdaFunction, NamedLambdaVariable, UnaryExpression}
+import org.apache.spark.sql.catalyst.expressions.codegen.{CodegenContext, ExprCode}
+import org.apache.spark.sql.catalyst.planning.ExtractEquiJoinKeys
+import org.apache.spark.sql.catalyst.plans.logical.{LogicalPlan, Subquery, Window}
+import org.apache.spark.sql.catalyst.rules.Rule
+import org.apache.spark.sql.types._
+
+/**
+ * We need to take care of special floating numbers (NaN and -0.0) in several places:
+ *   1. When compare values, different NaNs should be treated as same, `-0.0` and `0.0` should be
+ *      treated as same.
+ *   2. In GROUP BY, different NaNs should belong to the same group, -0.0 and 0.0 should belong
+ *      to the same group.
+ *   3. In join keys, different NaNs should be treated as same, `-0.0` and `0.0` should be
+ *      treated as same.
+ *   4. In window partition keys, different NaNs should be treated as same, `-0.0` and `0.0`
+ *      should be treated as same.
+ *
+ * Case 1 is fine, as we handle NaN and -0.0 well during comparison. For complex types, we
+ * recursively compare the fields/elements, so it's also fine.
+ *
+ * Case 2, 3 and 4 are problematic, as they compare `UnsafeRow` binary directly, and different
+ * NaNs have different binary representation, and the same thing happens for -0.0 and 0.0.
+ *
+ * This rule normalizes NaN and -0.0 in Window partition keys, Join keys and Aggregate grouping
+ * expressions.
+ */
+object NormalizeFloatingNumbers extends Rule[LogicalPlan] {
+
+  def apply(plan: LogicalPlan): LogicalPlan = plan match {
+    // A subquery will be rewritten into join later, and will go through this rule
+    // eventually. Here we skip subquery, as we only need to run this rule once.
+    case _: Subquery => plan
+
+    case _ => plan transform {
+      case w: Window if w.partitionSpec.exists(p => needNormalize(p.dataType)) =>
+        w.copy(partitionSpec = w.partitionSpec.map(normalize))
 
 Review comment:
   Nit. All the window expressions in the project list also refer to the partitionSpec. Should we also normalize these?

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