[GitHub] [arrow-datafusion] mingmwang commented on a diff in pull request #4192: add `propagate_empty_relation` optimizer rule

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

mingmwang commented on code in PR #4192:
URL: https://github.com/apache/arrow-datafusion/pull/4192#discussion_r1020895687


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datafusion/optimizer/src/propagate_empty_relation.rs:
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@@ -0,0 +1,178 @@
+// 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.
+
+use datafusion_common::Result;
+use datafusion_expr::logical_plan::LogicalPlan;
+use datafusion_expr::EmptyRelation;
+
+use crate::{utils, OptimizerConfig, OptimizerRule};
+
+/// Optimization rule that bottom-up to eliminate plan by propagating empty_relation.
+#[derive(Default)]
+pub struct PropagateEmptyRelation;
+
+impl PropagateEmptyRelation {
+    #[allow(missing_docs)]
+    pub fn new() -> Self {
+        Self {}
+    }
+}
+
+impl OptimizerRule for PropagateEmptyRelation {
+    fn optimize(
+        &self,
+        plan: &LogicalPlan,
+        optimizer_config: &mut OptimizerConfig,
+    ) -> Result<LogicalPlan> {
+        // optimize child plans first
+        let optimized_children_plan =
+            utils::optimize_children(self, plan, optimizer_config)?;
+        let optimized_plan_opt = match &optimized_children_plan {
+            LogicalPlan::Projection(_)
+            | LogicalPlan::Filter(_)
+            | LogicalPlan::Window(_)
+            | LogicalPlan::Sort(_)
+            | LogicalPlan::Join(_)

Review Comment:
   For Join, we need to be careful:
   For Inner join, if either side is empty, the Join is empty.
   For LeftOuter/LeftSemi/LeftAnti Join, only the left side is empty, the Join result is empty.
   For RightOuter/RightSemi/RightAnti Join, only the right side is empty, the Join result is empty.
   For Full Join, only both sides are empty, the Join result is empty.
   



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