viirya commented on a change in pull request #23390: [SPARK-26459][SQL] replace UpdateNullabilityInAttributeReferences with FixNullability URL: https://github.com/apache/spark/pull/23390#discussion_r245014290
########## File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/UpdateAttributeNullability.scala ########## @@ -0,0 +1,62 @@ +/* + * 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.analysis + +import org.apache.spark.sql.catalyst.expressions.{Attribute, AttributeMap} +import org.apache.spark.sql.catalyst.plans.logical.{LeafNode, LogicalPlan} +import org.apache.spark.sql.catalyst.rules.Rule + +/** + * Updates nullability of Attributes in a resolved LogicalPlan by using the nullability of + * corresponding Attributes of its children output Attributes. This step is needed because + * users can use a resolved AttributeReference in the Dataset API and outer joins + * can change the nullability of an AttribtueReference. Without this rule, a nullable column's + * nullable field can be actually set as non-nullable, which cause illegal optimization + * (e.g., NULL propagation) and wrong answers. + * See SPARK-13484 and SPARK-13801 for the concrete queries of this case. + * + * This rule should be executed again at the end of optimization phase, as optimizer may change Review comment: It sounds weird that in optimization phase we make correct nullability to wrong again. Can we have other way to solve it? ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected] With regards, Apache Git Services --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
