[feature](Nereids): Convert topn(x, 1) to max(x) (#26004)

fe/fe-core/src/main/java/org/apache/doris/nereids/rules/expression/ExpressionOptimization.java

@@ -26,6 +26,7 @@ import org.apache.doris.nereids.rules.expression.rules.SimplifyComparisonPredica
 import org.apache.doris.nereids.rules.expression.rules.SimplifyDecimalV3Comparison;
 import org.apache.doris.nereids.rules.expression.rules.SimplifyInPredicate;
 import org.apache.doris.nereids.rules.expression.rules.SimplifyRange;
+import org.apache.doris.nereids.rules.expression.rules.TopnToMax;
 
 import com.google.common.collect.ImmutableList;
 
@@ -44,7 +45,8 @@ public class ExpressionOptimization extends ExpressionRewrite {
             SimplifyRange.INSTANCE,
             OrToIn.INSTANCE,
             ArrayContainToArrayOverlap.INSTANCE,
-            CaseWhenToIf.INSTANCE
+            CaseWhenToIf.INSTANCE,
+            TopnToMax.INSTANCE
     );
     private static final ExpressionRuleExecutor EXECUTOR = new ExpressionRuleExecutor(OPTIMIZE_REWRITE_RULES);
 

fe/fe-core/src/main/java/org/apache/doris/nereids/rules/expression/rules/TopnToMax.java

@@ -0,0 +1,55 @@
+// 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.doris.nereids.rules.expression.rules;
+
+import org.apache.doris.nereids.rules.expression.ExpressionRewriteContext;
+import org.apache.doris.nereids.rules.expression.ExpressionRewriteRule;
+import org.apache.doris.nereids.trees.expressions.Expression;
+import org.apache.doris.nereids.trees.expressions.functions.agg.AggregateFunction;
+import org.apache.doris.nereids.trees.expressions.functions.agg.Max;
+import org.apache.doris.nereids.trees.expressions.functions.agg.TopN;
+import org.apache.doris.nereids.trees.expressions.literal.IntegerLikeLiteral;
+import org.apache.doris.nereids.trees.expressions.visitor.DefaultExpressionRewriter;
+
+/**
+ * Convert topn(x, 1) to max(x)
+ */
+public class TopnToMax extends DefaultExpressionRewriter<ExpressionRewriteContext> implements
+        ExpressionRewriteRule<ExpressionRewriteContext> {
+
+    public static final TopnToMax INSTANCE = new TopnToMax();
+
+    @Override
+    public Expression rewrite(Expression expr, ExpressionRewriteContext ctx) {
+        return expr.accept(this, null);
+    }
+
+    @Override
+    public Expression visitAggregateFunction(AggregateFunction aggregateFunction, ExpressionRewriteContext context) {
+        if (!(aggregateFunction instanceof TopN)) {
+            return aggregateFunction;
+        }
+        TopN topN = (TopN) aggregateFunction;
+        if (topN.arity() == 2 && topN.child(1) instanceof IntegerLikeLiteral
+                && ((IntegerLikeLiteral) topN.child(1)).getIntValue() == 1) {
+            return new Max(topN.child(0));
+        } else {
+            return aggregateFunction;
+        }
+    }
+}

fe/fe-core/src/test/java/org/apache/doris/nereids/rules/expression/rules/TopnToMaxTest.java

@@ -0,0 +1,40 @@
+// 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.doris.nereids.rules.expression.rules;
+
+import org.apache.doris.nereids.rules.expression.ExpressionRewriteTestHelper;
+import org.apache.doris.nereids.rules.expression.ExpressionRuleExecutor;
+import org.apache.doris.nereids.trees.expressions.Slot;
+import org.apache.doris.nereids.trees.expressions.SlotReference;
+import org.apache.doris.nereids.trees.expressions.functions.agg.Max;
+import org.apache.doris.nereids.trees.expressions.functions.agg.TopN;
+import org.apache.doris.nereids.trees.expressions.literal.Literal;
+import org.apache.doris.nereids.types.StringType;
+
+import com.google.common.collect.ImmutableList;
+import org.junit.jupiter.api.Test;
+
+class TopnToMaxTest extends ExpressionRewriteTestHelper {
+    @Test
+    void testSimplifyComparisonPredicateRule() {
+        executor = new ExpressionRuleExecutor(ImmutableList.of(TopnToMax.INSTANCE));
+
+        Slot slot = new SlotReference("a", StringType.INSTANCE);
+        assertRewrite(new TopN(slot, Literal.of(1)), new Max(slot));
+    }
+}

regression-test/data/nereids_p0/expression/topn_to_max.out

@@ -0,0 +1,8 @@
+-- This file is automatically generated. You should know what you did if you want to edit this
+-- !sql --
+1	1
+2	2
+
+-- !sql --
+2
+

regression-test/suites/nereids_p0/expression/topn_to_max.groovy

@@ -0,0 +1,49 @@
+// 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.
+
+suite("test_topn_to_max") {
+    sql 'set enable_nereids_planner=true'
+    sql 'set enable_fallback_to_original_planner=false'
+
+    sql 'drop table if exists test_topn_to_max;'
+
+    sql '''create table test_topn_to_max (k1 int, k2 string) distributed by hash(k1) buckets 3 properties('replication_num' = '1');'''
+    sql '''insert into test_topn_to_max values (1, "1"),  (2, "2");'''
+
+
+    order_qt_sql '''
+    select k1, topn(k2, 1)
+    from test_topn_to_max
+    group by k1;
+    '''
+    res = sql '''
+    explain rewritten plan select k1, max(k2)
+    from test_topn_to_max
+    group by k1;
+    '''
+    assertTrue(res.toString().contains("max"))
+
+    order_qt_sql '''
+    select topn(k2, 1)
+    from test_topn_to_max;
+    '''
+    res = sql '''
+    explain rewritten plan select max(k2)
+    from test_topn_to_max;
+    '''
+    assertTrue(res.toString().contains("max"))
+}