cloud-fan commented on code in PR #50192: URL: https://github.com/apache/spark/pull/50192#discussion_r1998636873
########## sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/ReassignAliasNamesWithCollations.scala: ########## @@ -0,0 +1,78 @@ +/* + * 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.{Alias, Cast, Expression, Literal} +import org.apache.spark.sql.catalyst.plans.logical.LogicalPlan +import org.apache.spark.sql.catalyst.rules.Rule +import org.apache.spark.sql.catalyst.trees.TreePattern.ALIAS +import org.apache.spark.sql.catalyst.util.{toPrettySQL, AUTO_GENERATED_ALIAS} +import org.apache.spark.sql.types.StringType + +/** + * Reassign [[Alias]] names for expression trees with collations. We need this rule because + * [[AliasResolution]] cannot easily detect if the expression nodes are properly casted to collated + * types or not, and sometimes assigns alias names before [[CollationTypeCoercion]] is run. + * + * For example, if we didn't have this rule: + * + * {{{ + * -- The output alias name is "(collate('a', UTF8_LCASE) < 'A' collate UTF8_LCASE)" + * SELECT 'a' COLLATE UTF8_LCASE < 'A'; + * + * -- The output alias name is "concat_ws(a, col1, col1)" + * SELECT CONCAT_WS('a', col1, col1) FROM VALUES ('a' COLLATE UTF8_LCASE); + * }}} + * + * In the second case literal 'a' does not have "collate" information after it because + * [[ResolveAliases]] runs before [[AnsiCombinedTypeCoercionRule]]. + */ +object ReassignAliasNamesWithCollations extends Rule[LogicalPlan] { + override def apply(plan: LogicalPlan): LogicalPlan = { + plan.resolveExpressionsWithPruning(_.containsPattern(ALIAS)) { + case a: Alias + if a.resolved && + a.metadata.contains(AUTO_GENERATED_ALIAS) && + hasNonDefaultCollationInTheSubtree(a.child) => + val newName = toPrettySQL(a.child) + if (newName != a.name) { + a.withName(newName) + } else { + a + } + } + } + + /** + * Detect if we have a non-default collation in the subtree under [[Alias]]. We only need to check + * [[Cast]] and [[Literal]], because only those expressions are affected by + * [[CollationTypeCoercion]]. + */ + private def hasNonDefaultCollationInTheSubtree(rootExpression: Expression) = { + rootExpression.exists { expression => + expression match { Review Comment: so this only checks the root node but does not recursively go into the expression tree? -- 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: reviews-unsubscr...@spark.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For additional commands, e-mail: reviews-h...@spark.apache.org
