gatorsmile commented on a change in pull request #25107: [SPARK-28344][SQL] detect ambiguous self-join and fail the query URL: https://github.com/apache/spark/pull/25107#discussion_r310374783
########## File path: sql/core/src/main/scala/org/apache/spark/sql/execution/analysis/DetectAmbiguousSelfJoin.scala ########## @@ -0,0 +1,159 @@ +/* + * 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.execution.analysis + +import scala.collection.mutable + +import org.apache.spark.sql.{AnalysisException, Column, Dataset} +import org.apache.spark.sql.catalyst.expressions.{AttributeReference, Cast, Equality, Expression, ExprId} +import org.apache.spark.sql.catalyst.plans.logical.{Join, LogicalPlan} +import org.apache.spark.sql.catalyst.rules.Rule +import org.apache.spark.sql.internal.SQLConf + +/** + * Detects ambiguous self-joins, so that we can fail the query instead of returning confusing + * results. + * + * Dataset column reference is simply an [[AttributeReference]] that is returned by `Dataset#col`. + * Most of time we don't need to do anything special, as [[AttributeReference]] can point to + * the column precisely. However, in case of self-join, the analyzer generates + * [[AttributeReference]] with new expr IDs for the right side plan of the join. If the Dataset + * column reference points to a column in the right side plan of a self-join, users will get + * unexpected result because the column reference can't match the newly generated + * [[AttributeReference]]. Review comment: In the description, we need to also document the metadata are removed by this rule. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to 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]
