the hidden column, result column id 0, would be the ts column of the outer...

the hidden column, result column id 0, would be the ts column of the outer query and inner query may not be sorted such as that diff then group by

src/query/src/qPlan.c

@@ -588,6 +588,12 @@ SArray* createExecOperatorPlan(SQueryAttr* pQueryAttr) {
         op = OP_Fill;
         taosArrayPush(plan, &op);
       }
+      // outer query order by support
+      int32_t orderColId = pQueryAttr->order.orderColId;
+      if (pQueryAttr->vgId == 0 && orderColId != INT32_MIN) {
+        op = OP_Order;
+        taosArrayPush(plan, &op);
+      }
     }
 
   } else if (pQueryAttr->groupbyColumn) {
@@ -658,7 +664,7 @@ SArray* createExecOperatorPlan(SQueryAttr* pQueryAttr) {
 
     // outer query order by support
     int32_t orderColId = pQueryAttr->order.orderColId;
-    if (pQueryAttr->vgId == 0 && orderColId != PRIMARYKEY_TIMESTAMP_COL_INDEX && orderColId != INT32_MIN) {
+    if (pQueryAttr->vgId == 0 && orderColId != INT32_MIN) {
       op = OP_Order;
       taosArrayPush(plan, &op);
     }