[fix](nereids) translate agg-dist

fe/fe-core/src/main/java/org/apache/doris/nereids/glue/translator/PhysicalPlanTranslator.java

@@ -227,10 +227,14 @@ public PlanFragment visitPhysicalHashAggregate(
                 .collect(Collectors.toCollection(ArrayList::new));
 
         PlanFragment currentFragment;
-        if (inputPlanFragment.getPlanRoot() instanceof ExchangeNode) {
-            Preconditions.checkState(aggregate.child() instanceof PhysicalDistribute,
-                    "When the ExchangeNode is child of PhysicalHashAggregate, "
-                            + "it should be created by PhysicalDistribute, but meet " + aggregate.child());
+        if (inputPlanFragment.getPlanRoot() instanceof ExchangeNode
+                && aggregate.child() instanceof PhysicalDistribute) {
+            //the exchange node is generated in two cases:
+            //  1. some nodes (e.g. sort node) need to gather data from multiple instances, and hence their gather phase
+            //     need an exchange node. For this type of exchange, their data partition is un_partitioned, do not
+            //     create a new plan fragment.
+            //  2. PhysicalDistribute node is translated to exchange node. PhysicalDistribute node means we need to
+            //     shuffle data, and we have to create a new plan fragment.
             ExchangeNode exchangeNode = (ExchangeNode) inputPlanFragment.getPlanRoot();
             Optional<List<Expression>> partitionExpressions = aggregate.getPartitionExpressions();
             PhysicalDistribute physicalDistribute = (PhysicalDistribute) aggregate.child();

regression-test/data/nereids_syntax_p0/agg_with_sort.out

@@ -0,0 +1,4 @@
+-- This file is automatically generated. You should know what you did if you want to edit this
+-- !select --
+0
+

regression-test/suites/nereids_syntax_p0/agg_with_sort.groovy

@@ -0,0 +1,38 @@
+// 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("agg_with_sort") {
+    sql "SET enable_nereids_planner=true"
+    sql "set enable_fallback_to_original_planner=false"
+    sql """
+        DROP TABLE IF EXISTS tbl
+       """
+
+    sql """CREATE TABLE IF NOT EXISTS tbl (a int not null, b int not null)
+        DISTRIBUTED BY HASH(a)
+        BUCKETS 1
+        PROPERTIES(
+            "replication_num"="1"
+        )
+        """
+    //make sure we can handle this sql pattern:
+    // agg -> exchange -> sort
+
+    qt_select """
+        select count(1) from (select a from tbl order by a desc) t;
+    """
+}