cloud-fan commented on a change in pull request #32072: URL: https://github.com/apache/spark/pull/32072#discussion_r616360942
########## File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/DecorrelateInnerQuery.scala ########## @@ -0,0 +1,484 @@ +/* + * 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._ +import org.apache.spark.sql.catalyst.expressions.SubExprUtils._ +import org.apache.spark.sql.catalyst.plans._ +import org.apache.spark.sql.catalyst.plans.logical._ + +/** + * Decorrelate the inner query by eliminating outer references and create domain joins. + * The implementation is based on the paper: Unnesting Arbitrary Queries by Thomas Neumann + * and Alfons Kemper. https://dl.gi.de/handle/20.500.12116/2418. + * + * A correlated subquery can be viewed as a "dependent" nested loop join between the outer and + * the inner query. For each row produced by the outer query, we bind the [[OuterReference]]s in + * in the inner query with the corresponding values in the row, and then evaluate the inner query. Review comment: nit: `in the inner query` -> `the inner query`. the line above ends with `in` -- 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] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
