[fix](projection)join node should always output at least one column

fe/fe-core/src/main/java/org/apache/doris/planner/HashJoinNode.java

@@ -301,14 +301,26 @@ public void initOutputSlotIds(Set<SlotId> requiredSlotIdSet, Analyzer analyzer)
                 outputTupleDescList.add(analyzer.getTupleDesc(tupleId));
             }
         }
+        SlotId firstMaterializedSlotId = null;
         for (TupleDescriptor tupleDescriptor : outputTupleDescList) {
             for (SlotDescriptor slotDescriptor : tupleDescriptor.getSlots()) {
-                if (slotDescriptor.isMaterialized()
-                        && (requiredSlotIdSet == null || requiredSlotIdSet.contains(slotDescriptor.getId()))) {
-                    outputSlotIds.add(slotDescriptor.getId());
+                if (slotDescriptor.isMaterialized()) {
+                    if ((requiredSlotIdSet == null || requiredSlotIdSet.contains(slotDescriptor.getId()))) {
+                        outputSlotIds.add(slotDescriptor.getId());
+                    }
+                    if (firstMaterializedSlotId == null) {
+                        firstMaterializedSlotId = slotDescriptor.getId();
+                    }
                 }
             }
         }
+
+        // be may be possible to output correct row number without any column data in future
+        // but for now, in order to have correct output row number, should keep at least one slot.
+        // use first materialized slot if outputSlotIds is empty.
+        if (outputSlotIds.isEmpty() && firstMaterializedSlotId != null) {
+            outputSlotIds.add(firstMaterializedSlotId);
+        }
         initHashOutputSlotIds(outputSlotIds, analyzer);
     }
 

regression-test/data/correctness_p0/test_join_with_projection.out

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

regression-test/suites/correctness_p0/test_join_with_projection.groovy

@@ -0,0 +1,82 @@
+// 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_join_with_projection") {
+    sql """
+        drop table if exists outerjoin_A;
+    """
+
+    sql """
+        drop table if exists outerjoin_B;
+    """
+
+    sql """
+        create table outerjoin_A ( a int not null )
+        ENGINE=OLAP
+        DISTRIBUTED BY HASH(a) BUCKETS 1
+        PROPERTIES (
+        "replication_allocation" = "tag.location.default: 1",
+        "in_memory" = "false",
+        "storage_format" = "V2"
+        );
+    """
+
+    sql """
+        create table outerjoin_B ( a int not null )
+        ENGINE=OLAP
+        DISTRIBUTED BY HASH(a) BUCKETS 1
+        PROPERTIES (
+        "replication_allocation" = "tag.location.default: 1",
+        "in_memory" = "false",
+        "storage_format" = "V2"
+        );
+    """
+
+    sql """
+        insert into outerjoin_A values( 1 );
+    """
+
+    sql """
+        insert into outerjoin_B values( 1 );
+    """
+
+    qt_select """
+        select
+            CASE
+            WHEN true THEN
+            1
+            ELSE 1
+            END AS c0
+        FROM 
+            (SELECT a AS c0
+            FROM outerjoin_A
+            ) AS subq_1
+        RIGHT JOIN 
+            (SELECT a AS c0
+            FROM outerjoin_B
+            ) AS subq_2
+            ON (subq_1.c0 = subq_2.c0 );
+    """
+
+    sql """
+        drop table if exists outerjoin_A;
+    """
+
+    sql """
+        drop table if exists outerjoin_B;
+    """
+}