crepererum commented on code in PR #7695: URL: https://github.com/apache/arrow-datafusion/pull/7695#discussion_r1352382911
########## datafusion/optimizer/src/eliminate_nested_union.rs: ########## @@ -0,0 +1,211 @@ +// 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. + +//! Optimizer rule to replace nested unions to single union. +use crate::{OptimizerConfig, OptimizerRule}; +use datafusion_common::Result; +use datafusion_expr::logical_plan::{LogicalPlan, Union}; + +use crate::optimizer::ApplyOrder; +use datafusion_expr::expr_rewriter::coerce_plan_expr_for_schema; +use std::sync::Arc; + +#[derive(Default)] +/// An optimization rule that replaces nested unions with a single union. +pub struct EliminateNestedUnion; + +impl EliminateNestedUnion { + #[allow(missing_docs)] + pub fn new() -> Self { + Self {} + } +} + +impl OptimizerRule for EliminateNestedUnion { + fn try_optimize( + &self, + plan: &LogicalPlan, + _config: &dyn OptimizerConfig, + ) -> Result<Option<LogicalPlan>> { + // TODO: Add optimization for nested distinct unions. Review Comment: at one point (maybe as a TODO) we probably should also remove unions that have only a single child since they are basically a no-op/pass-through. Not sure if this should be an separate optimizer rule or if this should be done in this rule. -- 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]
