vli-databricks commented on code in PR #36527: URL: https://github.com/apache/spark/pull/36527#discussion_r872918192
########## sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/RewriteNonAggregateFirst.scala: ########## @@ -0,0 +1,72 @@ +/* + * 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.{Alias, Literal} +import org.apache.spark.sql.catalyst.expressions.aggregate.{AggregateExpression, First} +import org.apache.spark.sql.catalyst.plans.logical._ +import org.apache.spark.sql.catalyst.rules.Rule +import org.apache.spark.sql.catalyst.trees.TreePattern.FIRST +import org.apache.spark.sql.types.IntegerType + +/** + * Rewrite aggregate plan with a single [[First]] function when grouping is absent. In such a case + * the query is equivalent to simple projection with limit 1. + * + * Input Pseudo-Query: + * {{{ + * SELECT FIRST(col) FROM table + * }}} + * + * Rewritten Query: + * {{{ + * SELECT col FROM table LIMIT 1 + * }}} + * + * Note that using IGNORE NULLS with [[First]] blocks rewrite logic since projection with NOT NULL + * filter might return different result than [[First]] if all values are NULL. + */ +object RewriteNonAggregateFirst extends Rule[LogicalPlan] { + override def apply(plan: LogicalPlan): LogicalPlan = { + plan.transformWithPruning(_.containsPattern(FIRST), ruleId) { + case agg: Aggregate if isNonAggregateFirst(agg) => + rewriteNonAggregateFirstToProject(agg) + } + } + + private def isNonAggregateFirst(agg: Aggregate): Boolean = { + agg.aggregateExpressions.length == 1 && agg.groupingExpressions.isEmpty + } + + private def rewriteNonAggregateFirstToProject(agg: Aggregate): LogicalPlan = { + var skipRewrite = false + val projectList = agg.aggregateExpressions.map { + case alias: Alias => Review Comment: redid since the logic changed. -- 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]
