[GitHub] [calcite] amaliujia commented on a change in pull request #2329: [CALCITE-3221] Add a sort-merge union algorithm

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

amaliujia commented on a change in pull request #2329:
URL: https://github.com/apache/calcite/pull/2329#discussion_r560523613



##########
File path: core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableMergeUnion.java
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@@ -0,0 +1,128 @@
+/*
+ * 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.Ord;
+import org.apache.calcite.linq4j.tree.BlockBuilder;
+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.RelOptCost;
+import org.apache.calcite.plan.RelOptPlanner;
+import org.apache.calcite.plan.RelTraitSet;
+import org.apache.calcite.rel.RelCollation;
+import org.apache.calcite.rel.RelCollationTraitDef;
+import org.apache.calcite.rel.RelNode;
+import org.apache.calcite.rel.metadata.RelMetadataQuery;
+import org.apache.calcite.util.BuiltInMethod;
+import org.apache.calcite.util.Pair;
+import org.apache.calcite.util.Util;
+
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/** Implementation of {@link org.apache.calcite.rel.core.Union} in
+ * {@link org.apache.calcite.adapter.enumerable.EnumerableConvention enumerable calling convention}.
+ * Performs a union (or union all) of all its inputs (which must be already sorted),
+ * respecting the order. */
+public class EnumerableMergeUnion extends EnumerableUnion {
+
+  protected EnumerableMergeUnion(RelOptCluster cluster, RelTraitSet traitSet, List<RelNode> inputs,

Review comment:
       Are inputs ordering checked somewhere? E.g. check collations of inputs?




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