[GitHub] [arrow-datafusion] returnString commented on a change in pull request #213: Add rule to eliminate `LIMIT 0` and replace it with an `EmptyRelation`

[GitBox <gi...@apache.org>]

returnString commented on a change in pull request #213:
URL: https://github.com/apache/arrow-datafusion/pull/213#discussion_r621498784



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File path: datafusion/src/optimizer/eliminate_limit.rs
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@@ -0,0 +1,122 @@
+// 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 `LIMIT 0` on a plan with an empty relation.
+//! This saves time in planning and executing the query.
+use crate::error::Result;
+use crate::logical_plan::LogicalPlan;
+use crate::optimizer::optimizer::OptimizerRule;
+
+use super::utils;
+
+/// Optimization rule that replaces LIMIT 0 with an [LogicalPlan::EmptyRelation]
+pub struct EliminateLimit {}

Review comment:
       Could this just be a unit struct, i.e. `pub struct EliminateLimit;` or is the intent to support optional future config in the struct? Not super-familiar with the optimiser setup.




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