[GitHub] [calcite] zabetak commented on a change in pull request #1020: [CALCITE-2812] Add algebraic operators to allow expressing recursive queries (Ruben Quesada Lopez)

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zabetak commented on a change in pull request #1020: [CALCITE-2812] Add algebraic operators to allow expressing recursive queries (Ruben Quesada Lopez)
URL: https://github.com/apache/calcite/pull/1020#discussion_r272256796
 
 

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 File path: core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableRecursiveUnion.java
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+/*
+ * 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.calcite.adapter.enumerable;
+
+import org.apache.calcite.linq4j.tree.BlockBuilder;
+import org.apache.calcite.linq4j.tree.DeclarationStatement;
+import org.apache.calcite.linq4j.tree.Expression;
+import org.apache.calcite.linq4j.tree.Expressions;
+import org.apache.calcite.linq4j.tree.ParameterExpression;
+import org.apache.calcite.plan.RelOptCluster;
+import org.apache.calcite.plan.RelTraitSet;
+import org.apache.calcite.rel.RelNode;
+import org.apache.calcite.rel.RelWriter;
+import org.apache.calcite.rel.core.SetOp;
+import org.apache.calcite.rel.core.Union;
+import org.apache.calcite.schema.Table;
+import org.apache.calcite.schema.impl.TransientTable;
+import org.apache.calcite.util.BuiltInMethod;
+
+import java.util.List;
+
+
+/**
+ * Implementation of Recursive Union in
+ * {@link EnumerableConvention enumerable calling convention}.
+ */
+public class EnumerableRecursiveUnion extends Union implements EnumerableRel {
 
 Review comment:
   I like the new design but before going forward let's see what the others have to say. Just a few additional information for those following the discussion.
   
   There has been a small debate on the name of the RepeatUnion. `Iterate` and `RecursiveUnion` were the other names that were abandoned. 
   
   Although `Iterate`, initially seemed to be a nice abstraction, at the end of the day the description of what it should do was a union of the results of its inputs with the particularity that we always start from the `seedRel` and we repeatedly union the `iterativeRel`.
   
   `RecursiveUnion` also seemed nice, since it is a named also used by Postgres, and fits well with the `RECURSIVE` keyword of SQL. However, it gives the false impression that the operator does some kind of recursion which is not the case. 

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