dtenedor commented on code in PR #36527: URL: https://github.com/apache/spark/pull/36527#discussion_r872705861
########## 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 Review Comment: Yeah, the optimization triggers in a small subset of cases. So we don't want to add a lot of complexity or compilation time. With the ideas suggested in this review, I think we can simplify the code for the rule implementation. And the pruning takes place in O(1) with bitmaps so it should not impose any compilation time unless the query actually contains FIRST aggregate function(s), and even then, very little. -- 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]
