[GitHub] [calcite] herunkang2018 commented on a diff in pull request #3418: [CALCITE-5994] Add optimization rule to remove Sort when its input's row number is less or equal to one

["herunkang2018 (via GitHub)" <gi...@apache.org>]

herunkang2018 commented on code in PR #3418:
URL: https://github.com/apache/calcite/pull/3418#discussion_r1330831977


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core/src/main/java/org/apache/calcite/rel/rules/SortRemoveRedundantRule.java:
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@@ -0,0 +1,77 @@
+/*
+ * 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.rel.rules;
+
+import org.apache.calcite.plan.RelOptRuleCall;
+import org.apache.calcite.plan.RelRule;
+import org.apache.calcite.rel.core.Sort;
+
+import org.immutables.value.Value;
+
+/**
+ * Planner rule that removes
+ * the redundant {@link org.apache.calcite.rel.core.Sort} if its input
+ * max row number is less than or equal to one.
+ *
+ * <p> For example:
+ * <blockquote><pre>{@code
+ *  select max(totalprice) from orders order by 1}
+ *  </pre></blockquote>
+ *
+ * <p> could be converted to
+ * <blockquote><pre>{@code
+ *  select max(totalprice) from orders}
+ *  </pre></blockquote>
+ *
+ * @see CoreRules#SORT_REMOVE_REDUNDANT
+ */
+@Value.Enclosing
+public class SortRemoveRedundantRule
+    extends RelRule<SortRemoveRedundantRule.Config>
+    implements TransformationRule {
+  protected SortRemoveRedundantRule(final SortRemoveRedundantRule.Config config) {
+    super(config);
+  }
+
+  @Override public void onMatch(final RelOptRuleCall call) {
+    final Sort sort = call.rel(0);
+    if (sort.offset != null || sort.fetch != null) {
+      // Don't remove sort if would also remove OFFSET or LIMIT.

Review Comment:
   Minor comment, this description is not clear. I would use 'Don't remove sort if it has explicit OFFSET and LIMIT'.



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