Github user nsyca commented on a diff in the pull request: https://github.com/apache/spark/pull/16233#discussion_r95665834 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/view.scala --- @@ -0,0 +1,80 @@ +/* + * 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.AnalysisException +import org.apache.spark.sql.catalyst.CatalystConf +import org.apache.spark.sql.catalyst.expressions.{Alias, Attribute, Cast} +import org.apache.spark.sql.catalyst.plans.logical.{LogicalPlan, Project, View} +import org.apache.spark.sql.catalyst.rules.Rule + +/** + * This file defines analysis rules related to views. + */ + +/** + * Make sure that a view's child plan produces the view's output attributes. We wrap the child + * with a Project and add an alias for each output attribute. The attributes are resolved by + * name. This should be only done after the batch of Resolution, because the view attributes are + * not completely resolved during the batch of Resolution. + */ +case class AliasViewChild(conf: CatalystConf) extends Rule[LogicalPlan] { + override def apply(plan: LogicalPlan): LogicalPlan = plan resolveOperators { + case v @ View(_, output, child) if child.resolved => + val resolver = conf.resolver + val newOutput = output.map { attr => + val originAttr = findAttributeByName(attr.name, child.output, resolver) + // The dataType of the output attributes may be not the same with that of the view output, + // so we should cast the attribute to the dataType of the view output attribute. If the + // cast can't perform, will throw an AnalysisException. --- End diff -- I am curious in which scenario that the data types of the child will not match the view. Do you have an example? Or this is just a safety net. If it is, can it be done as an assertion instead?
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