MaxGekk commented on code in PR #49029: URL: https://github.com/apache/spark/pull/49029#discussion_r1877610602
########## sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/resolver/AttributeScopeStack.scala: ########## @@ -0,0 +1,89 @@ +/* + * 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.resolver + +import java.util.ArrayDeque + +import org.apache.spark.sql.catalyst.expressions.{Attribute, AttributeSet} + +/** + * The [[AttributeScopeStack]] is used to validate that the attribute which was encountered by the + * [[ExpressionResolutionValidator]] is in the current operator's visibility scope. We use + * [[AttributeSet]] as scope implementation here to check the equality of attributes based on their + * expression IDs. + * + * E.g. for the following SQL query: + * {{{ + * SELECT a, a, a + col2 FROM (SELECT col1 as a, col2 FROM VALUES (1, 2)); + * }}} + * + * Having the following logical plan: + * {{{ + * Project [a#2, a#2, (a#2 + col2#1) AS (a + col2)#3] + * +- SubqueryAlias __auto_generated_subquery_name + * +- Project [col1#0 AS a#2, col2#1] + * +- LocalRelation [col1#0, col2#1] + * }}} + * + * The [[LocalRelation]] outputs attributes with IDs #0 and #1, which can be referenced by the lower + * [[Project]]. This [[Project]] produces a new attribute ID #2 for an alias and retains the old + * ID #1 for col2. The upper [[Project]] references `a` twice using the same ID #2 and produces a + * new ID #3 for an alias of `a + col2`. + */ +class AttributeScopeStack { + private val stack = new ArrayDeque[AttributeSet] + push() + + /** + * Get the relevant attribute scope in the context of the current operator. + */ + def top: AttributeSet = { + stack.peek() + } + + /** + * Overwrite current relevant scope with a sequence of attributes which is an output of some + * operator. `attributes` can have duplicate IDs if the output of the operator contains multiple + * occurencies of the same attribute. Review Comment: ```suggestion * occurrences of the same attribute. ``` -- 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. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
