diff --git a/source/common/src/tdatablock.c b/source/common/src/tdatablock.c
index 160756d981..46d1c51c64 100644
--- a/source/common/src/tdatablock.c
+++ b/source/common/src/tdatablock.c
@@ -1216,7 +1216,7 @@ SSDataBlock* createOneDataBlock(const SSDataBlock* pDataBlock, bool copyData) {
 
   pBlock->info.numOfCols = numOfCols;
   pBlock->info.hasVarCol = pDataBlock->info.hasVarCol;
-  pBlock->info.rowSize = pDataBlock->info.rows;
+  pBlock->info.rowSize = pDataBlock->info.rowSize;
 
   for (int32_t i = 0; i < numOfCols; ++i) {
     SColumnInfoData  colInfo = {0};
diff --git a/source/libs/command/inc/commandInt.h b/source/libs/command/inc/commandInt.h
index 100e35bc3c..a3755a174e 100644
--- a/source/libs/command/inc/commandInt.h
+++ b/source/libs/command/inc/commandInt.h
@@ -47,6 +47,9 @@ extern "C" {
 #define EXPLAIN_TIME_WINDOWS_FORMAT "Time Window: interval=%" PRId64 "%c offset=%" PRId64 "%c sliding=%" PRId64 "%c"
 #define EXPLAIN_WINDOW_FORMAT "Window: gap=%" PRId64
 #define EXPLAIN_RATIO_TIME_FORMAT "Ratio: %f"
+#define EXPLAIN_MERGE_FORMAT "Merge"
+#define EXPLAIN_MERGE_KEYS_FORMAT "Merge Key: "
+
 #define EXPLAIN_PLANNING_TIME_FORMAT "Planning Time: %.3f ms"
 #define EXPLAIN_EXEC_TIME_FORMAT "Execution Time: %.3f ms"
 
diff --git a/source/libs/command/src/explain.c b/source/libs/command/src/explain.c
index 99ff4d406c..347fb326bb 100644
--- a/source/libs/command/src/explain.c
+++ b/source/libs/command/src/explain.c
@@ -173,6 +173,11 @@ int32_t qExplainGenerateResChildren(SPhysiNode *pNode, SExplainGroup *group, SNo
       pPhysiChildren = partitionPhysiNode->node.pChildren;
       break;
     }
+    case QUERY_NODE_PHYSICAL_PLAN_MERGE: {
+      SMergePhysiNode *mergePhysiNode = (SMergePhysiNode *)pNode;
+      pPhysiChildren = mergePhysiNode->node.pChildren;
+      break;
+    }
     default:
       qError("not supported physical node type %d", pNode->type);
       QRY_ERR_RET(TSDB_CODE_QRY_APP_ERROR);
@@ -857,6 +862,50 @@ int32_t qExplainResNodeToRowsImpl(SExplainResNode *pResNode, SExplainCtx *ctx, i
       }
       break;
     }
+    case QUERY_NODE_PHYSICAL_PLAN_MERGE: {
+      SMergePhysiNode *pMergeNode = (SMergePhysiNode *)pNode;
+      EXPLAIN_ROW_NEW(level, EXPLAIN_MERGE_FORMAT);
+      EXPLAIN_ROW_APPEND(EXPLAIN_LEFT_PARENTHESIS_FORMAT);
+      if (pResNode->pExecInfo) {
+        QRY_ERR_RET(qExplainBufAppendExecInfo(pResNode->pExecInfo, tbuf, &tlen));
+        EXPLAIN_ROW_APPEND(EXPLAIN_BLANK_FORMAT);
+      }
+
+      SDataBlockDescNode *pDescNode = pMergeNode->node.pOutputDataBlockDesc;
+      EXPLAIN_ROW_APPEND(EXPLAIN_COLUMNS_FORMAT, nodesGetOutputNumFromSlotList(pDescNode->pSlots));
+      EXPLAIN_ROW_APPEND(EXPLAIN_BLANK_FORMAT);
+      EXPLAIN_ROW_APPEND(EXPLAIN_WIDTH_FORMAT, pDescNode->totalRowSize);
+      EXPLAIN_ROW_APPEND(EXPLAIN_RIGHT_PARENTHESIS_FORMAT);
+      EXPLAIN_ROW_END();
+      QRY_ERR_RET(qExplainResAppendRow(ctx, tbuf, tlen, level));
+
+      if (verbose) {
+        EXPLAIN_ROW_NEW(level + 1, EXPLAIN_OUTPUT_FORMAT);
+        EXPLAIN_ROW_APPEND(EXPLAIN_COLUMNS_FORMAT,
+                           nodesGetOutputNumFromSlotList(pMergeNode->node.pOutputDataBlockDesc->pSlots));
+        EXPLAIN_ROW_APPEND(EXPLAIN_BLANK_FORMAT);
+        EXPLAIN_ROW_APPEND(EXPLAIN_WIDTH_FORMAT, pMergeNode->node.pOutputDataBlockDesc->outputRowSize);
+        EXPLAIN_ROW_END();
+        QRY_ERR_RET(qExplainResAppendRow(ctx, tbuf, tlen, level + 1));
+
+        EXPLAIN_ROW_NEW(level + 1, EXPLAIN_MERGE_KEYS_FORMAT);
+        for (int32_t i = 0; i < LIST_LENGTH(pMergeNode->pMergeKeys); ++i) {
+          SOrderByExprNode *ptn = nodesListGetNode(pMergeNode->pMergeKeys, i);
+          EXPLAIN_ROW_APPEND("%s ", nodesGetNameFromColumnNode(ptn->pExpr));
+        }
+        EXPLAIN_ROW_END();
+        QRY_ERR_RET(qExplainResAppendRow(ctx, tbuf, tlen, level + 1));
+
+        if (pMergeNode->node.pConditions) {
+          EXPLAIN_ROW_NEW(level + 1, EXPLAIN_FILTER_FORMAT);
+          QRY_ERR_RET(nodesNodeToSQL(pMergeNode->node.pConditions, tbuf + VARSTR_HEADER_SIZE,
+                                     TSDB_EXPLAIN_RESULT_ROW_SIZE, &tlen));
+          EXPLAIN_ROW_END();
+          QRY_ERR_RET(qExplainResAppendRow(ctx, tbuf, tlen, level + 1));
+        }
+      }
+      break;
+    }    
     default:
       qError("not supported physical node type %d", pNode->type);
       return TSDB_CODE_QRY_APP_ERROR;
diff --git a/source/libs/executor/inc/executorimpl.h b/source/libs/executor/inc/executorimpl.h
index 9b8b9dca26..3dcf2a7c0c 100644
--- a/source/libs/executor/inc/executorimpl.h
+++ b/source/libs/executor/inc/executorimpl.h
@@ -787,7 +787,7 @@ SOperatorInfo* createIndefinitOutputOperatorInfo(SOperatorInfo* downstream, SPhy
 SOperatorInfo* createProjectOperatorInfo(SOperatorInfo* downstream, SExprInfo* pExprInfo, int32_t num, SSDataBlock* pResBlock, SLimit* pLimit, SLimit* pSlimit, SNode* pCondition, SExecTaskInfo* pTaskInfo);
 SOperatorInfo *createSortOperatorInfo(SOperatorInfo* downstream, SSDataBlock* pResBlock, SArray* pSortInfo, SExprInfo* pExprInfo, int32_t numOfCols,
                                       SArray* pIndexMap, SExecTaskInfo* pTaskInfo);
-SOperatorInfo* createMultiwaySortMergeOperatorInfo(SOperatorInfo** downStreams, int32_t numStreams,
+SOperatorInfo* createMultiwaySortMergeOperatorInfo(SOperatorInfo** downStreams, int32_t numStreams, SSDataBlock* pInputBlock,
                                                    SSDataBlock* pResBlock, SArray* pSortInfo, SArray* pColMatchColInfo,
                                                    SExecTaskInfo* pTaskInfo);
 SOperatorInfo* createSortedMergeOperatorInfo(SOperatorInfo** downstream, int32_t numOfDownstream, SExprInfo* pExprInfo, int32_t num, SArray* pSortInfo, SArray* pGroupInfo, SExecTaskInfo* pTaskInfo);
diff --git a/source/libs/executor/inc/tsort.h b/source/libs/executor/inc/tsort.h
index c8b1b3ee51..fd3581e2bf 100644
--- a/source/libs/executor/inc/tsort.h
+++ b/source/libs/executor/inc/tsort.h
@@ -130,6 +130,12 @@ bool tsortIsNullVal(STupleHandle* pVHandle, int32_t colId);
  */
 void* tsortGetValue(STupleHandle* pVHandle, int32_t colId);
 
+/**
+ *
+ * @param pVHandle
+ * @return
+ */
+uint64_t tsortGetGroupId(STupleHandle* pVHandle);
 /**
  *
  * @param pSortHandle
diff --git a/source/libs/executor/src/executorimpl.c b/source/libs/executor/src/executorimpl.c
index 464fb5c957..ea54ae472d 100644
--- a/source/libs/executor/src/executorimpl.c
+++ b/source/libs/executor/src/executorimpl.c
@@ -4666,8 +4666,9 @@ SOperatorInfo* createOperatorTree(SPhysiNode* pPhyNode, SExecTaskInfo* pTaskInfo
     int32_t numOfOutputCols = 0;
     SArray* pColList =
         extractColMatchInfo(pMergePhyNode->pTargets, pDescNode, &numOfOutputCols, pTaskInfo, COL_MATCH_FROM_SLOT_ID);
-
-    pOptr = createMultiwaySortMergeOperatorInfo(ops, size, pResBlock, sortInfo, pColList, pTaskInfo);
+    SPhysiNode* pChildNode = (SPhysiNode*)nodesListGetNode(pPhyNode->pChildren, 0);
+    SSDataBlock* pInputDataBlock = createResDataBlock(pChildNode->pOutputDataBlockDesc);
+    pOptr = createMultiwaySortMergeOperatorInfo(ops, size, pInputDataBlock, pResBlock, sortInfo, pColList, pTaskInfo);
   } else if (QUERY_NODE_PHYSICAL_PLAN_MERGE_SESSION == type) {
     SSessionWinodwPhysiNode* pSessionNode = (SSessionWinodwPhysiNode*)pPhyNode;
 
diff --git a/source/libs/executor/src/sortoperator.c b/source/libs/executor/src/sortoperator.c
index c84d4491af..95f9514b07 100644
--- a/source/libs/executor/src/sortoperator.c
+++ b/source/libs/executor/src/sortoperator.c
@@ -84,7 +84,6 @@ void appendOneRowToDataBlock(SSDataBlock* pBlock, STupleHandle* pTupleHandle) {
 SSDataBlock* getSortedBlockData(SSortHandle* pHandle, SSDataBlock* pDataBlock, int32_t capacity,
                                 SArray* pColMatchInfo) {
   blockDataCleanup(pDataBlock);
-  ASSERT(taosArrayGetSize(pColMatchInfo) == pDataBlock->info.numOfCols);
 
   SSDataBlock* p = tsortGetSortedDataBlock(pHandle);
   if (p == NULL) {
@@ -230,7 +229,12 @@ typedef struct SMultiwaySortMergeOperatorInfo {
   SSortHandle* pSortHandle;
   SArray*      pColMatchInfo;  // for index map from table scan output
 
+  SSDataBlock* pInputBlock;
   int64_t startTs;  // sort start time
+
+  bool  hasGroupId;
+  uint64_t groupId;
+  STupleHandle *prefetchedTuple;
 } SMultiwaySortMergeOperatorInfo;
 
 int32_t doOpenMultiwaySortMergeOperator(SOperatorInfo* pOperator) {
@@ -246,14 +250,14 @@ int32_t doOpenMultiwaySortMergeOperator(SOperatorInfo* pOperator) {
   int32_t numOfBufPage = pInfo->sortBufSize / pInfo->bufPageSize;
 
   pInfo->pSortHandle = tsortCreateSortHandle(pInfo->pSortInfo, pInfo->pColMatchInfo, SORT_MULTISOURCE_MERGE,
-                                             pInfo->bufPageSize, numOfBufPage, NULL, pTaskInfo->id.str);
+                                             pInfo->bufPageSize, numOfBufPage, pInfo->pInputBlock, pTaskInfo->id.str);
 
   tsortSetFetchRawDataFp(pInfo->pSortHandle, loadNextDataBlock, NULL, NULL);
 
   for (int32_t i = 0; i < pOperator->numOfDownstream; ++i) {
-    SSortSource ps = {0};
-    ps.param = pOperator->pDownstream[i];
-    tsortAddSource(pInfo->pSortHandle, &ps);
+    SSortSource* ps = taosMemoryCalloc(1, sizeof(SSortSource));
+    ps->param = pOperator->pDownstream[i];
+    tsortAddSource(pInfo->pSortHandle, ps);
   }
 
   int32_t code = tsortOpen(pInfo->pSortHandle);
@@ -269,6 +273,70 @@ int32_t doOpenMultiwaySortMergeOperator(SOperatorInfo* pOperator) {
   return TSDB_CODE_SUCCESS;
 }
 
+SSDataBlock* getMultiwaySortedBlockData(SSortHandle* pHandle, SSDataBlock* pDataBlock, int32_t capacity,
+                                SArray* pColMatchInfo, SMultiwaySortMergeOperatorInfo* pInfo) {
+  blockDataCleanup(pDataBlock);
+
+  SSDataBlock* p = tsortGetSortedDataBlock(pHandle);
+  if (p == NULL) {
+    return NULL;
+  }
+
+  blockDataEnsureCapacity(p, capacity);
+
+  while (1) {
+
+    STupleHandle* pTupleHandle = NULL;
+    if (pInfo->prefetchedTuple == NULL) {
+      pTupleHandle = tsortNextTuple(pHandle);
+    } else {
+      pTupleHandle = pInfo->prefetchedTuple;
+      pInfo->prefetchedTuple = NULL;
+    }
+
+    if (pTupleHandle == NULL) {
+      break;
+    }
+
+    uint64_t tupleGroupId = tsortGetGroupId(pTupleHandle);
+    if (!pInfo->hasGroupId) {
+      pInfo->groupId = tupleGroupId;
+      pInfo->hasGroupId = true;
+      appendOneRowToDataBlock(p, pTupleHandle);
+    } else if (pInfo->groupId == tupleGroupId) {
+      appendOneRowToDataBlock(p, pTupleHandle);
+    } else {
+      pInfo->prefetchedTuple = pTupleHandle;
+      pInfo->groupId = tupleGroupId;
+      break;
+    }
+
+    if (p->info.rows >= capacity) {
+      break;
+    }
+
+  }
+
+  if (p->info.rows > 0) {
+    int32_t numOfCols = taosArrayGetSize(pColMatchInfo);
+    for (int32_t i = 0; i < numOfCols; ++i) {
+      SColMatchInfo* pmInfo = taosArrayGet(pColMatchInfo, i);
+      ASSERT(pmInfo->matchType == COL_MATCH_FROM_SLOT_ID);
+
+      SColumnInfoData* pSrc = taosArrayGet(p->pDataBlock, pmInfo->srcSlotId);
+      SColumnInfoData* pDst = taosArrayGet(pDataBlock->pDataBlock, pmInfo->targetSlotId);
+      colDataAssign(pDst, pSrc, p->info.rows);
+    }
+
+    pDataBlock->info.rows = p->info.rows;
+    pDataBlock->info.capacity = p->info.rows;
+  }
+
+  blockDataDestroy(p);
+  return (pDataBlock->info.rows > 0) ? pDataBlock : NULL;
+}
+
+
 SSDataBlock* doMultiwaySortMerge(SOperatorInfo* pOperator) {
   if (pOperator->status == OP_EXEC_DONE) {
     return NULL;
@@ -283,7 +351,11 @@ SSDataBlock* doMultiwaySortMerge(SOperatorInfo* pOperator) {
   }
 
   SSDataBlock* pBlock =
-      getSortedBlockData(pInfo->pSortHandle, pInfo->binfo.pRes, pOperator->resultInfo.capacity, pInfo->pColMatchInfo);
+      getMultiwaySortedBlockData(pInfo->pSortHandle,
+                         pInfo->binfo.pRes,
+                         pOperator->resultInfo.capacity,
+                         pInfo->pColMatchInfo,
+                                 pInfo);
 
   if (pBlock != NULL) {
     pOperator->resultInfo.totalRows += pBlock->info.rows;
@@ -296,6 +368,7 @@ SSDataBlock* doMultiwaySortMerge(SOperatorInfo* pOperator) {
 void destroyMultiwaySortMergeOperatorInfo(void* param, int32_t numOfOutput) {
   SMultiwaySortMergeOperatorInfo * pInfo = (SMultiwaySortMergeOperatorInfo*)param;
   pInfo->binfo.pRes = blockDataDestroy(pInfo->binfo.pRes);
+  pInfo->pInputBlock = blockDataDestroy(pInfo->pInputBlock);
 
   taosArrayDestroy(pInfo->pSortInfo);
   taosArrayDestroy(pInfo->pColMatchInfo);
@@ -313,7 +386,7 @@ int32_t getMultiwaySortMergeExplainExecInfo(SOperatorInfo* pOptr, void** pOptrEx
   return TSDB_CODE_SUCCESS;
 }
 
-SOperatorInfo* createMultiwaySortMergeOperatorInfo(SOperatorInfo** downStreams, int32_t numStreams,
+SOperatorInfo* createMultiwaySortMergeOperatorInfo(SOperatorInfo** downStreams, int32_t numStreams, SSDataBlock* pInputBlock,
                                                    SSDataBlock* pResBlock, SArray* pSortInfo, SArray* pColMatchColInfo,
                                                    SExecTaskInfo* pTaskInfo) {
   SMultiwaySortMergeOperatorInfo* pInfo = taosMemoryCalloc(1, sizeof(SMultiwaySortMergeOperatorInfo));
@@ -330,6 +403,7 @@ SOperatorInfo* createMultiwaySortMergeOperatorInfo(SOperatorInfo** downStreams,
 
   pInfo->pSortInfo = pSortInfo;
   pInfo->pColMatchInfo = pColMatchColInfo;
+  pInfo->pInputBlock = pInputBlock;
   pOperator->name = "MultiwaySortMerge";
   pOperator->operatorType = QUERY_NODE_PHYSICAL_PLAN_MERGE;
   pOperator->blocking = true;
diff --git a/source/libs/executor/src/tsort.c b/source/libs/executor/src/tsort.c
index 7581836d59..846da4a32a 100644
--- a/source/libs/executor/src/tsort.c
+++ b/source/libs/executor/src/tsort.c
@@ -225,6 +225,10 @@ static int32_t sortComparInit(SMsortComparParam* cmpParam, SArray* pSources, int
     for (int32_t i = 0; i < cmpParam->numOfSources; ++i) {
       SSortSource* pSource = cmpParam->pSources[i];
       pSource->src.pBlock = pHandle->fetchfp(pSource->param);
+      if (pSource->src.pBlock == NULL) {
+        pSource->src.rowIndex = -1;
+        ++pHandle->numOfCompletedSources;
+      }
     }
   }
 
@@ -361,13 +365,21 @@ int32_t msortComparFn(const void *pLeft, const void *pRight, void *param) {
 
     bool leftNull  = false;
     if (pLeftColInfoData->hasNull) {
-      leftNull = colDataIsNull(pLeftColInfoData, pLeftBlock->info.rows, pLeftSource->src.rowIndex, pLeftBlock->pBlockAgg[pOrder->slotId]);
+      if (pLeftBlock->pBlockAgg == NULL) {
+        leftNull = colDataIsNull_s(pLeftColInfoData, pLeftSource->src.rowIndex);
+      } else {
+        leftNull = colDataIsNull(pLeftColInfoData, pLeftBlock->info.rows, pLeftSource->src.rowIndex, pLeftBlock->pBlockAgg[i]);
+      }
     }
 
     SColumnInfoData* pRightColInfoData = TARRAY_GET_ELEM(pRightBlock->pDataBlock, pOrder->slotId);
     bool rightNull = false;
     if (pRightColInfoData->hasNull) {
-      rightNull = colDataIsNull(pRightColInfoData, pRightBlock->info.rows, pRightSource->src.rowIndex, pRightBlock->pBlockAgg[pOrder->slotId]);
+      if (pLeftBlock->pBlockAgg == NULL) {
+        rightNull = colDataIsNull_s(pRightColInfoData, pRightSource->src.rowIndex);
+      } else {
+        rightNull = colDataIsNull(pRightColInfoData, pRightBlock->info.rows, pRightSource->src.rowIndex, pRightBlock->pBlockAgg[i]);
+      }
     }
 
     if (leftNull && rightNull) {
@@ -408,7 +420,7 @@ static int32_t doInternalMergeSort(SSortHandle* pHandle) {
 
   pHandle->totalElapsed = taosGetTimestampUs() - pHandle->startTs;
   qDebug("%s %d rounds mergesort required to complete the sort, first-round sorted data size:%"PRIzu", sort elapsed:%"PRId64", total elapsed:%"PRId64,
-         pHandle->idStr, (int32_t) (sortPass + 1), getTotalBufSize(pHandle->pBuf), pHandle->sortElapsed, pHandle->totalElapsed);
+         pHandle->idStr, (int32_t) (sortPass + 1), pHandle->pBuf ? getTotalBufSize(pHandle->pBuf) : 0, pHandle->sortElapsed, pHandle->totalElapsed);
 
   int32_t numOfRows = blockDataGetCapacityInRow(pHandle->pDataBlock, pHandle->pageSize);
   blockDataEnsureCapacity(pHandle->pDataBlock, numOfRows);
@@ -697,6 +709,10 @@ void* tsortGetValue(STupleHandle* pVHandle, int32_t colIndex) {
   return colDataGetData(pColInfo, pVHandle->rowIndex);
 }
 
+uint64_t tsortGetGroupId(STupleHandle* pVHandle) {
+  return pVHandle->pBlock->info.groupId;
+}
+
 SSortExecInfo tsortGetSortExecInfo(SSortHandle* pHandle) {
   SSortExecInfo info = {0};
 
diff --git a/source/libs/planner/src/planSpliter.c b/source/libs/planner/src/planSpliter.c
index e5c81eda4b..a7f53bb752 100644
--- a/source/libs/planner/src/planSpliter.c
+++ b/source/libs/planner/src/planSpliter.c
@@ -166,8 +166,8 @@ static bool stbSplNeedSplit(bool streamQuery, SLogicNode* pNode) {
       }
       return !stbSplHasGatherExecFunc(pWindow->pFuncs) && stbSplHasMultiTbScan(streamQuery, pNode);
     }
-    // case QUERY_NODE_LOGIC_PLAN_SORT:
-    //   return stbSplHasMultiTbScan(streamQuery, pNode);
+    case QUERY_NODE_LOGIC_PLAN_SORT:
+      return stbSplHasMultiTbScan(streamQuery, pNode);
     case QUERY_NODE_LOGIC_PLAN_SCAN:
       return stbSplIsMultiTbScan(streamQuery, (SScanLogicNode*)pNode);
     default:
diff --git a/tests/script/tsim/query/scalarNull.sim b/tests/script/tsim/query/scalarNull.sim
index b08ac1d3d9..07bd5e57cd 100644
--- a/tests/script/tsim/query/scalarNull.sim
+++ b/tests/script/tsim/query/scalarNull.sim
@@ -66,6 +66,7 @@ if $rows != 0 then
   return -1
 endi
 sql select * from tb1 where null;
+print $rows
 if $rows != 0 then
   return -1
 endi