diff --git a/source/libs/executor/inc/executorimpl.h b/source/libs/executor/inc/executorimpl.h
index a6bc4dfe9759351cecf4dee0d7a39438d6c50867..9b9a1ef259936881ec80e5a0a406053eed9ce34c 100644
--- a/source/libs/executor/inc/executorimpl.h
+++ b/source/libs/executor/inc/executorimpl.h
@@ -776,7 +776,6 @@ typedef struct STimeSliceOperatorInfo {
   SArray*              pPrevRow;     // SArray<SGroupValue>
   SArray*              pNextRow;     // SArray<SGroupValue>
   SArray*              pLinearInfo;  // SArray<SFillLinearInfo>
-  bool                 fillLastPoint;
   bool                 isPrevRowSet;
   bool                 isNextRowSet;
   int32_t              fillType;      // fill type
diff --git a/source/libs/executor/inc/tfill.h b/source/libs/executor/inc/tfill.h
index ed019be767b63b9ec641ea25b86670d1cdd4974e..2d8df81dbd5318b80258a2b71d16acf3f9880a8b 100644
--- a/source/libs/executor/inc/tfill.h
+++ b/source/libs/executor/inc/tfill.h
@@ -36,7 +36,8 @@ typedef struct SFillColInfo {
 typedef struct SFillLinearInfo {
   SPoint  start;
   SPoint  end;
-  bool    hasNull;
+  bool    isStartSet;
+  bool    isEndSet;
   int16_t type;
   int32_t bytes;
 } SFillLinearInfo;
diff --git a/source/libs/executor/src/timewindowoperator.c b/source/libs/executor/src/timewindowoperator.c
index 0573450be23a0f408d119694207d01ee07b83250..fc78f8a20dd6c13fcc30462ba511f7ec6f9d9c24 100644
--- a/source/libs/executor/src/timewindowoperator.c
+++ b/source/libs/executor/src/timewindowoperator.c
@@ -1942,10 +1942,8 @@ static void doKeepPrevRows(STimeSliceOperatorInfo* pSliceInfo, const SSDataBlock
   for (int32_t i = 0; i < numOfCols; ++i) {
     SColumnInfoData* pColInfoData = taosArrayGet(pBlock->pDataBlock, i);
 
-    // null data should not be kept since it can not be used to perform interpolation
-    if (!colDataIsNull_s(pColInfoData, i)) {
-      SGroupKeys* pkey = taosArrayGet(pSliceInfo->pPrevRow, i);
-
+    SGroupKeys* pkey = taosArrayGet(pSliceInfo->pPrevRow, i);
+    if (!colDataIsNull_s(pColInfoData, rowIndex)) {
       pkey->isNull = false;
       char* val = colDataGetData(pColInfoData, rowIndex);
       if (!IS_VAR_DATA_TYPE(pkey->type)) {
@@ -1953,6 +1951,8 @@ static void doKeepPrevRows(STimeSliceOperatorInfo* pSliceInfo, const SSDataBlock
       } else {
         memcpy(pkey->pData, val, varDataLen(val));
       }
+    } else {
+      pkey->isNull = true;
     }
   }
 
@@ -1964,10 +1964,8 @@ static void doKeepNextRows(STimeSliceOperatorInfo* pSliceInfo, const SSDataBlock
   for (int32_t i = 0; i < numOfCols; ++i) {
     SColumnInfoData* pColInfoData = taosArrayGet(pBlock->pDataBlock, i);
 
-    // null data should not be kept since it can not be used to perform interpolation
-    if (!colDataIsNull_s(pColInfoData, i)) {
-      SGroupKeys* pkey = taosArrayGet(pSliceInfo->pNextRow, i);
-
+    SGroupKeys* pkey = taosArrayGet(pSliceInfo->pNextRow, i);
+    if (!colDataIsNull_s(pColInfoData, rowIndex)) {
       pkey->isNull = false;
       char* val = colDataGetData(pColInfoData, rowIndex);
       if (!IS_VAR_DATA_TYPE(pkey->type)) {
@@ -1975,50 +1973,51 @@ static void doKeepNextRows(STimeSliceOperatorInfo* pSliceInfo, const SSDataBlock
       } else {
         memcpy(pkey->pData, val, varDataLen(val));
       }
+    } else {
+      pkey->isNull = true;
     }
   }
 
   pSliceInfo->isNextRowSet = true;
 }
 
-static void doKeepLinearInfo(STimeSliceOperatorInfo* pSliceInfo, const SSDataBlock* pBlock, int32_t rowIndex,
-                             bool isLastRow) {
+static void doKeepLinearInfo(STimeSliceOperatorInfo* pSliceInfo, const SSDataBlock* pBlock, int32_t rowIndex) {
   int32_t numOfCols = taosArrayGetSize(pBlock->pDataBlock);
-  bool    fillLastPoint = pSliceInfo->fillLastPoint;
   for (int32_t i = 0; i < numOfCols; ++i) {
     SColumnInfoData* pColInfoData = taosArrayGet(pBlock->pDataBlock, i);
     SColumnInfoData* pTsCol = taosArrayGet(pBlock->pDataBlock, pSliceInfo->tsCol.slotId);
     SFillLinearInfo* pLinearInfo = taosArrayGet(pSliceInfo->pLinearInfo, i);
 
-    // null data should not be kept since it can not be used to perform interpolation
-    if (!colDataIsNull_s(pColInfoData, i)) {
-      if (isLastRow) {
+    // null value is represented by using key = INT64_MIN for now.
+    // TODO: optimize to ignore null values for linear interpolation.
+    if (!pLinearInfo->isStartSet) {
+      if (!colDataIsNull_s(pColInfoData, rowIndex)) {
         pLinearInfo->start.key = *(int64_t*)colDataGetData(pTsCol, rowIndex);
         memcpy(pLinearInfo->start.val, colDataGetData(pColInfoData, rowIndex), pLinearInfo->bytes);
-      } else if (fillLastPoint) {
+      }
+      pLinearInfo->isStartSet = true;
+    } else if (!pLinearInfo->isEndSet) {
+      if (!colDataIsNull_s(pColInfoData, rowIndex)) {
         pLinearInfo->end.key = *(int64_t*)colDataGetData(pTsCol, rowIndex);
         memcpy(pLinearInfo->end.val, colDataGetData(pColInfoData, rowIndex), pLinearInfo->bytes);
-      } else {
-        pLinearInfo->start.key = *(int64_t*)colDataGetData(pTsCol, rowIndex);
-        pLinearInfo->end.key = *(int64_t*)colDataGetData(pTsCol, rowIndex + 1);
-
-        char* val;
-        val = colDataGetData(pColInfoData, rowIndex);
-        memcpy(pLinearInfo->start.val, val, pLinearInfo->bytes);
-        val = colDataGetData(pColInfoData, rowIndex + 1);
-        memcpy(pLinearInfo->end.val, val, pLinearInfo->bytes);
       }
-
-      pLinearInfo->hasNull = false;
+      pLinearInfo->isEndSet = true;
     } else {
-      pLinearInfo->hasNull = true;
+      pLinearInfo->start.key = pLinearInfo->end.key;
+      memcpy(pLinearInfo->start.val, pLinearInfo->end.val, pLinearInfo->bytes);
+
+      if (!colDataIsNull_s(pColInfoData, rowIndex)) {
+        pLinearInfo->end.key = *(int64_t*)colDataGetData(pTsCol, rowIndex);
+        memcpy(pLinearInfo->end.val, colDataGetData(pColInfoData, rowIndex), pLinearInfo->bytes);
+      } else {
+        pLinearInfo->end.key = INT64_MIN;
+      }
     }
   }
 
-  pSliceInfo->fillLastPoint = isLastRow;
 }
 
-static void genInterpolationResult(STimeSliceOperatorInfo* pSliceInfo, SExprSupp* pExprSup, SSDataBlock* pResBlock) {
+static bool genInterpolationResult(STimeSliceOperatorInfo* pSliceInfo, SExprSupp* pExprSup, SSDataBlock* pResBlock, bool beforeTs) {
   int32_t rows = pResBlock->info.rows;
   blockDataEnsureCapacity(pResBlock, rows + 1);
   // todo set the correct primary timestamp column
@@ -2037,7 +2036,6 @@ static void genInterpolationResult(STimeSliceOperatorInfo* pSliceInfo, SExprSupp
     }
 
     int32_t srcSlot = pExprInfo->base.pParam[0].pCol->slotId;
-    // SColumnInfoData* pSrc = taosArrayGet(pBlock->pDataBlock, srcSlot);
     switch (pSliceInfo->fillType) {
       case TSDB_FILL_NULL: {
         colDataAppendNULL(pDst, rows);
@@ -2069,21 +2067,26 @@ static void genInterpolationResult(STimeSliceOperatorInfo* pSliceInfo, SExprSupp
         SPoint start = pLinearInfo->start;
         SPoint end = pLinearInfo->end;
         SPoint current = {.key = pSliceInfo->current};
-        current.val = taosMemoryCalloc(pLinearInfo->bytes, 1);
 
-        // before interp range, do not fill
-        if (start.key == INT64_MIN || end.key == INT64_MAX) {
+        // do not interpolate before ts range, only increate pSliceInfo->current
+        if (beforeTs && !pLinearInfo->isEndSet) {
+          return true;
+        }
+
+        if (!pLinearInfo->isStartSet || !pLinearInfo->isEndSet) {
           hasInterp = false;
           break;
         }
 
-        if (pLinearInfo->hasNull) {
+        if (start.key == INT64_MIN || end.key == INT64_MIN) {
           colDataAppendNULL(pDst, rows);
-        } else {
-          taosGetLinearInterpolationVal(&current, pLinearInfo->type, &start, &end, pLinearInfo->type);
-          colDataAppend(pDst, rows, (char*)current.val, false);
+          break;
         }
 
+        current.val = taosMemoryCalloc(pLinearInfo->bytes, 1);
+        taosGetLinearInterpolationVal(&current, pLinearInfo->type, &start, &end, pLinearInfo->type);
+        colDataAppend(pDst, rows, (char*)current.val, false);
+
         taosMemoryFree(current.val);
         break;
       }
@@ -2094,7 +2097,11 @@ static void genInterpolationResult(STimeSliceOperatorInfo* pSliceInfo, SExprSupp
         }
 
         SGroupKeys* pkey = taosArrayGet(pSliceInfo->pPrevRow, srcSlot);
-        colDataAppend(pDst, rows, pkey->pData, false);
+        if (pkey->isNull == false) {
+          colDataAppend(pDst, rows, pkey->pData, false);
+        } else {
+          colDataAppendNULL(pDst, rows);
+        }
         break;
       }
 
@@ -2105,7 +2112,11 @@ static void genInterpolationResult(STimeSliceOperatorInfo* pSliceInfo, SExprSupp
         }
 
         SGroupKeys* pkey = taosArrayGet(pSliceInfo->pNextRow, srcSlot);
-        colDataAppend(pDst, rows, pkey->pData, false);
+        if (pkey->isNull == false) {
+          colDataAppend(pDst, rows, pkey->pData, false);
+        } else {
+          colDataAppendNULL(pDst, rows);
+        }
         break;
       }
 
@@ -2118,8 +2129,40 @@ static void genInterpolationResult(STimeSliceOperatorInfo* pSliceInfo, SExprSupp
   if (hasInterp) {
     pResBlock->info.rows += 1;
   }
+
+  return hasInterp;
 }
 
+static void addCurrentRowToResult(STimeSliceOperatorInfo* pSliceInfo, SExprSupp* pExprSup, SSDataBlock* pResBlock,
+                                  SSDataBlock* pSrcBlock, int32_t index) {
+  blockDataEnsureCapacity(pResBlock, pResBlock->info.rows + 1);
+  for (int32_t j = 0; j < pExprSup->numOfExprs; ++j) {
+    SExprInfo* pExprInfo = &pExprSup->pExprInfo[j];
+
+    int32_t          dstSlot = pExprInfo->base.resSchema.slotId;
+    SColumnInfoData* pDst = taosArrayGet(pResBlock->pDataBlock, dstSlot);
+
+    if (IS_TIMESTAMP_TYPE(pExprInfo->base.resSchema.type)) {
+      colDataAppend(pDst, pResBlock->info.rows, (char*)&pSliceInfo->current, false);
+    } else {
+      int32_t          srcSlot = pExprInfo->base.pParam[0].pCol->slotId;
+      SColumnInfoData* pSrc = taosArrayGet(pSrcBlock->pDataBlock, srcSlot);
+
+      if (colDataIsNull_s(pSrc, index)) {
+        colDataAppendNULL(pDst, pResBlock->info.rows);
+        continue;
+      }
+
+      char* v = colDataGetData(pSrc, index);
+      colDataAppend(pDst, pResBlock->info.rows, v, false);
+    }
+  }
+
+  pResBlock->info.rows += 1;
+  return;
+}
+
+
 static int32_t initPrevRowsKeeper(STimeSliceOperatorInfo* pInfo, SSDataBlock* pBlock) {
   if (pInfo->pPrevRow != NULL) {
     return TSDB_CODE_SUCCESS;
@@ -2190,24 +2233,19 @@ static int32_t initFillLinearInfo(STimeSliceOperatorInfo* pInfo, SSDataBlock* pB
 
     SFillLinearInfo linearInfo = {0};
     linearInfo.start.key = INT64_MIN;
-    linearInfo.end.key = INT64_MAX;
+    linearInfo.end.key = INT64_MIN;
     linearInfo.start.val = taosMemoryCalloc(1, pColInfo->info.bytes);
     linearInfo.end.val = taosMemoryCalloc(1, pColInfo->info.bytes);
-    linearInfo.hasNull = false;
+    linearInfo.isStartSet = false;
+    linearInfo.isEndSet = false;
     linearInfo.type = pColInfo->info.type;
     linearInfo.bytes = pColInfo->info.bytes;
     taosArrayPush(pInfo->pLinearInfo, &linearInfo);
   }
 
-  pInfo->fillLastPoint = false;
-
   return TSDB_CODE_SUCCESS;
 }
 
-static bool needToFillLastPoint(STimeSliceOperatorInfo* pSliceInfo) {
-  return (pSliceInfo->fillLastPoint == true && pSliceInfo->fillType == TSDB_FILL_LINEAR);
-}
-
 static int32_t initKeeperInfo(STimeSliceOperatorInfo* pInfo, SSDataBlock* pBlock) {
   int32_t code;
   code = initPrevRowsKeeper(pInfo, pBlock);
@@ -2263,195 +2301,73 @@ static SSDataBlock* doTimeslice(SOperatorInfo* pOperator) {
     for (int32_t i = 0; i < pBlock->info.rows; ++i) {
       int64_t ts = *(int64_t*)colDataGetData(pTsCol, i);
 
-      if (i == 0 && needToFillLastPoint(pSliceInfo)) {  // first row in current block
-        doKeepLinearInfo(pSliceInfo, pBlock, i, false);
-        while (pSliceInfo->current < ts && pSliceInfo->current <= pSliceInfo->win.ekey) {
-          genInterpolationResult(pSliceInfo, &pOperator->exprSupp, pResBlock);
-          pSliceInfo->current =
-              taosTimeAdd(pSliceInfo->current, pInterval->interval, pInterval->intervalUnit, pInterval->precision);
-        }
-      }
-
       if (pSliceInfo->current > pSliceInfo->win.ekey) {
         setOperatorCompleted(pOperator);
         break;
       }
 
       if (ts == pSliceInfo->current) {
-        blockDataEnsureCapacity(pResBlock, pResBlock->info.rows + 1);
-        for (int32_t j = 0; j < pOperator->exprSupp.numOfExprs; ++j) {
-          SExprInfo* pExprInfo = &pOperator->exprSupp.pExprInfo[j];
+        addCurrentRowToResult(pSliceInfo, &pOperator->exprSupp, pResBlock, pBlock, i);
 
-          int32_t          dstSlot = pExprInfo->base.resSchema.slotId;
-          SColumnInfoData* pDst = taosArrayGet(pResBlock->pDataBlock, dstSlot);
-
-          if (IS_TIMESTAMP_TYPE(pExprInfo->base.resSchema.type)) {
-            colDataAppend(pDst, pResBlock->info.rows, (char*)&pSliceInfo->current, false);
-          } else {
-            int32_t          srcSlot = pExprInfo->base.pParam[0].pCol->slotId;
-            SColumnInfoData* pSrc = taosArrayGet(pBlock->pDataBlock, srcSlot);
-
-            if (colDataIsNull_s(pSrc, i)) {
-              colDataAppendNULL(pDst, pResBlock->info.rows);
-              continue;
-            }
-
-            char* v = colDataGetData(pSrc, i);
-            colDataAppend(pDst, pResBlock->info.rows, v, false);
-          }
-        }
-
-        pResBlock->info.rows += 1;
         doKeepPrevRows(pSliceInfo, pBlock, i);
+        doKeepLinearInfo(pSliceInfo, pBlock, i);
 
-        // for linear interpolation, always fill value between this and next points;
-        // if its the first point in data block, also fill values between previous(if there's any) and this point;
-        // if its the last point in data block, no need to fill, but reserve this point as the start value and do
-        // the interpolation when processing next data block.
-        if (pSliceInfo->fillType == TSDB_FILL_LINEAR) {
-          pSliceInfo->current =
-              taosTimeAdd(pSliceInfo->current, pInterval->interval, pInterval->intervalUnit, pInterval->precision);
-          if (i < pBlock->info.rows - 1) {
-            doKeepLinearInfo(pSliceInfo, pBlock, i, false);
-            int64_t nextTs = *(int64_t*)colDataGetData(pTsCol, i + 1);
-            if (nextTs > pSliceInfo->current) {
-              while (pSliceInfo->current < nextTs && pSliceInfo->current <= pSliceInfo->win.ekey) {
-                genInterpolationResult(pSliceInfo, &pOperator->exprSupp, pResBlock);
-                pSliceInfo->current = taosTimeAdd(pSliceInfo->current, pInterval->interval, pInterval->intervalUnit,
-                                                  pInterval->precision);
-              }
-
-              if (pSliceInfo->current > pSliceInfo->win.ekey) {
-                setOperatorCompleted(pOperator);
-                break;
-              }
-            }
-          } else {  // it is the last row of current block
-            // store ts value as start, and calculate interp value when processing next block
-            doKeepLinearInfo(pSliceInfo, pBlock, i, true);
-          }
-        } else {  // non-linear interpolation
-          pSliceInfo->current =
-              taosTimeAdd(pSliceInfo->current, pInterval->interval, pInterval->intervalUnit, pInterval->precision);
-          if (pSliceInfo->current > pSliceInfo->win.ekey) {
-            setOperatorCompleted(pOperator);
-            break;
-          }
+        pSliceInfo->current =
+            taosTimeAdd(pSliceInfo->current, pInterval->interval, pInterval->intervalUnit, pInterval->precision);
+        if (pSliceInfo->current > pSliceInfo->win.ekey) {
+          setOperatorCompleted(pOperator);
+          break;
         }
       } else if (ts < pSliceInfo->current) {
         // in case of interpolation window starts and ends between two datapoints, fill(prev) need to interpolate
         doKeepPrevRows(pSliceInfo, pBlock, i);
-
-        if (pSliceInfo->fillType == TSDB_FILL_LINEAR) {
-          // no need to increate pSliceInfo->current here
-          // pSliceInfo->current =
-          //    taosTimeAdd(pSliceInfo->current, pInterval->interval, pInterval->intervalUnit, pInterval->precision);
-          if (i < pBlock->info.rows - 1) {
-            doKeepLinearInfo(pSliceInfo, pBlock, i, false);
-            int64_t nextTs = *(int64_t*)colDataGetData(pTsCol, i + 1);
-            if (nextTs > pSliceInfo->current) {
-              while (pSliceInfo->current < nextTs && pSliceInfo->current <= pSliceInfo->win.ekey) {
-                genInterpolationResult(pSliceInfo, &pOperator->exprSupp, pResBlock);
-                pSliceInfo->current = taosTimeAdd(pSliceInfo->current, pInterval->interval, pInterval->intervalUnit,
-                                                  pInterval->precision);
-              }
-
-              if (pSliceInfo->current > pSliceInfo->win.ekey) {
-                setOperatorCompleted(pOperator);
+        doKeepLinearInfo(pSliceInfo, pBlock, i);
+
+        if (i < pBlock->info.rows - 1) {
+          // in case of interpolation window starts and ends between two datapoints, fill(next) need to interpolate
+          doKeepNextRows(pSliceInfo, pBlock, i + 1);
+          int64_t nextTs = *(int64_t*)colDataGetData(pTsCol, i + 1);
+          if (nextTs > pSliceInfo->current) {
+            while (pSliceInfo->current < nextTs && pSliceInfo->current <= pSliceInfo->win.ekey) {
+              if (!genInterpolationResult(pSliceInfo, &pOperator->exprSupp, pResBlock, false) && pSliceInfo->fillType == TSDB_FILL_LINEAR) {
                 break;
+              } else {
+                pSliceInfo->current =
+                    taosTimeAdd(pSliceInfo->current, pInterval->interval, pInterval->intervalUnit, pInterval->precision);
               }
             }
-          } else {
-            // store ts value as start, and calculate interp value when processing next block
-            doKeepLinearInfo(pSliceInfo, pBlock, i, true);
-          }
-        } else {  // non-linear interpolation
-          if (i < pBlock->info.rows - 1) {
-            // in case of interpolation window starts and ends between two datapoints, fill(next) need to interpolate
-            doKeepNextRows(pSliceInfo, pBlock, i + 1);
-            int64_t nextTs = *(int64_t*)colDataGetData(pTsCol, i + 1);
-            if (nextTs > pSliceInfo->current) {
-              while (pSliceInfo->current < nextTs && pSliceInfo->current <= pSliceInfo->win.ekey) {
-                genInterpolationResult(pSliceInfo, &pOperator->exprSupp, pResBlock);
-                pSliceInfo->current = taosTimeAdd(pSliceInfo->current, pInterval->interval, pInterval->intervalUnit,
-                                                  pInterval->precision);
-              }
 
-              if (pSliceInfo->current > pSliceInfo->win.ekey) {
-                setOperatorCompleted(pOperator);
-                break;
-              }
-            } else {
-              // ignore current row, and do nothing
+            if (pSliceInfo->current > pSliceInfo->win.ekey) {
+              setOperatorCompleted(pOperator);
+              break;
             }
-          } else {  // it is the last row of current block
-            doKeepPrevRows(pSliceInfo, pBlock, i);
+          } else {
+            // ignore current row, and do nothing
           }
+        } else {  // it is the last row of current block
+          doKeepPrevRows(pSliceInfo, pBlock, i);
         }
       } else {  // ts > pSliceInfo->current
         // in case of interpolation window starts and ends between two datapoints, fill(next) need to interpolate
         doKeepNextRows(pSliceInfo, pBlock, i);
+        doKeepLinearInfo(pSliceInfo, pBlock, i);
 
         while (pSliceInfo->current < ts && pSliceInfo->current <= pSliceInfo->win.ekey) {
-          genInterpolationResult(pSliceInfo, &pOperator->exprSupp, pResBlock);
-          pSliceInfo->current =
-              taosTimeAdd(pSliceInfo->current, pInterval->interval, pInterval->intervalUnit, pInterval->precision);
+          if (!genInterpolationResult(pSliceInfo, &pOperator->exprSupp, pResBlock, true) && pSliceInfo->fillType == TSDB_FILL_LINEAR) {
+            break;
+          } else {
+            pSliceInfo->current =
+                taosTimeAdd(pSliceInfo->current, pInterval->interval, pInterval->intervalUnit, pInterval->precision);
+          }
         }
 
         // add current row if timestamp match
         if (ts == pSliceInfo->current && pSliceInfo->current <= pSliceInfo->win.ekey) {
-          blockDataEnsureCapacity(pResBlock, pResBlock->info.rows + 1);
-          for (int32_t j = 0; j < pOperator->exprSupp.numOfExprs; ++j) {
-            SExprInfo* pExprInfo = &pOperator->exprSupp.pExprInfo[j];
-
-            int32_t          dstSlot = pExprInfo->base.resSchema.slotId;
-            SColumnInfoData* pDst = taosArrayGet(pResBlock->pDataBlock, dstSlot);
-
-            if (IS_TIMESTAMP_TYPE(pExprInfo->base.resSchema.type)) {
-              colDataAppend(pDst, pResBlock->info.rows, (char*)&pSliceInfo->current, false);
-            } else {
-              int32_t          srcSlot = pExprInfo->base.pParam[0].pCol->slotId;
-              SColumnInfoData* pSrc = taosArrayGet(pBlock->pDataBlock, srcSlot);
-
-              if (colDataIsNull_s(pSrc, i)) {
-                colDataAppendNULL(pDst, pResBlock->info.rows);
-                continue;
-              }
-
-              char* v = colDataGetData(pSrc, i);
-              colDataAppend(pDst, pResBlock->info.rows, v, false);
-            }
-          }
-
-          pResBlock->info.rows += 1;
+          addCurrentRowToResult(pSliceInfo, &pOperator->exprSupp, pResBlock, pBlock, i);
           doKeepPrevRows(pSliceInfo, pBlock, i);
 
-          if (pSliceInfo->fillType == TSDB_FILL_LINEAR) {
-            pSliceInfo->current =
-                taosTimeAdd(pSliceInfo->current, pInterval->interval, pInterval->intervalUnit, pInterval->precision);
-            if (i < pBlock->info.rows - 1) {
-              doKeepLinearInfo(pSliceInfo, pBlock, i, false);
-              int64_t nextTs = *(int64_t*)colDataGetData(pTsCol, i + 1);
-              if (nextTs > pSliceInfo->current) {
-                while (pSliceInfo->current < nextTs && pSliceInfo->current <= pSliceInfo->win.ekey) {
-                  genInterpolationResult(pSliceInfo, &pOperator->exprSupp, pResBlock);
-                  pSliceInfo->current = taosTimeAdd(pSliceInfo->current, pInterval->interval, pInterval->intervalUnit,
-                                                    pInterval->precision);
-                }
-
-                if (pSliceInfo->current > pSliceInfo->win.ekey) {
-                  setOperatorCompleted(pOperator);
-                  break;
-                }
-              }
-            } else {  // it is the last row of current block
-              // store ts value as start, and calculate interp value when processing next block
-              doKeepLinearInfo(pSliceInfo, pBlock, i, true);
-            }
-          } else {  // non-linear interpolation
-            pSliceInfo->current =
-                taosTimeAdd(pSliceInfo->current, pInterval->interval, pInterval->intervalUnit, pInterval->precision);
-          }
+          pSliceInfo->current =
+              taosTimeAdd(pSliceInfo->current, pInterval->interval, pInterval->intervalUnit, pInterval->precision);
         }
 
         if (pSliceInfo->current > pSliceInfo->win.ekey) {
@@ -2466,7 +2382,7 @@ static SSDataBlock* doTimeslice(SOperatorInfo* pOperator) {
   // except for fill(next), fill(linear)
   while (pSliceInfo->current <= pSliceInfo->win.ekey && pSliceInfo->fillType != TSDB_FILL_NEXT &&
          pSliceInfo->fillType != TSDB_FILL_LINEAR) {
-    genInterpolationResult(pSliceInfo, &pOperator->exprSupp, pResBlock);
+    genInterpolationResult(pSliceInfo, &pOperator->exprSupp, pResBlock, false);
     pSliceInfo->current =
         taosTimeAdd(pSliceInfo->current, pInterval->interval, pInterval->intervalUnit, pInterval->precision);
   }
diff --git a/tests/system-test/2-query/interp.py b/tests/system-test/2-query/interp.py
index ce6b85c1cff7cbe263453db1e2c286f80f53ddb0..ce57357abda6564238362bcb861abab5e92f3947 100644
--- a/tests/system-test/2-query/interp.py
+++ b/tests/system-test/2-query/interp.py
@@ -18,6 +18,7 @@ class TDTestCase:
     def run(self):
         dbname = "db"
         tbname = "tb"
+        tbname1 = "tb1"
         stbname = "stb"
         ctbname1 = "ctb1"
         ctbname2 = "ctb2"
@@ -38,8 +39,6 @@ class TDTestCase:
         tdSql.execute(f"insert into {dbname}.{tbname} values ('2020-02-01 00:00:10', 10, 10, 10, 10, 10.0, 10.0, true, 'varchar', 'nchar')")
         tdSql.execute(f"insert into {dbname}.{tbname} values ('2020-02-01 00:00:15', 15, 15, 15, 15, 15.0, 15.0, true, 'varchar', 'nchar')")
 
-        tdSql.execute(f"insert into {dbname}.{tbname} (ts) values (now)")
-
         tdLog.printNoPrefix("==========step3:fill null")
 
         ## {. . .}
@@ -247,7 +246,7 @@ class TDTestCase:
 
         ## {. . .}
         tdSql.query(f"select interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:04', '2020-02-01 00:00:16') every(1s) fill(next)")
-        tdSql.checkRows(13)
+        tdSql.checkRows(12)
         tdSql.checkData(0, 0, 5)
         tdSql.checkData(1, 0, 5)
         tdSql.checkData(2, 0, 10)
@@ -297,21 +296,21 @@ class TDTestCase:
 
         ## ..{.}
         tdSql.query(f"select interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:13', '2020-02-01 00:00:17') every(1s) fill(next)")
-        tdSql.checkRows(5)
+        tdSql.checkRows(3)
         tdSql.checkData(0, 0, 15)
         tdSql.checkData(1, 0, 15)
         tdSql.checkData(2, 0, 15)
 
         ## ... {}
         tdSql.query(f"select interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:16', '2020-02-01 00:00:19') every(1s) fill(next)")
-        tdSql.checkRows(4)
+        tdSql.checkRows(0)
 
 
         tdLog.printNoPrefix("==========step7:fill linear")
 
         ## {. . .}
         tdSql.query(f"select interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:04', '2020-02-01 00:00:16') every(1s) fill(linear)")
-        tdSql.checkRows(12)
+        tdSql.checkRows(11)
         tdSql.checkData(0, 0, 5)
         tdSql.checkData(1, 0, 6)
         tdSql.checkData(2, 0, 7)
@@ -354,7 +353,7 @@ class TDTestCase:
 
         ## ..{.}
         tdSql.query(f"select interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:13', '2020-02-01 00:00:17') every(1s) fill(linear)")
-        tdSql.checkRows(5)
+        tdSql.checkRows(3)
         tdSql.checkData(0, 0, 13)
         tdSql.checkData(1, 0, 14)
         tdSql.checkData(2, 0, 15)
@@ -512,7 +511,7 @@ class TDTestCase:
         tdSql.checkData(8, 0, '2020-02-01 00:00:12.000')
 
         tdSql.query(f"select _irowts,interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:04', '2020-02-01 00:00:16') every(1s) fill(next)")
-        tdSql.checkRows(13)
+        tdSql.checkRows(12)
         tdSql.checkCols(2)
 
         tdSql.checkData(0, 0, '2020-02-01 00:00:04.000')
@@ -555,7 +554,7 @@ class TDTestCase:
         tdSql.checkData(8, 0, '2020-02-01 00:00:12.000')
 
         tdSql.query(f"select _irowts,interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:04', '2020-02-01 00:00:16') every(1s) fill(linear)")
-        tdSql.checkRows(12)
+        tdSql.checkRows(11)
         tdSql.checkCols(2)
 
         tdSql.checkData(0, 0, '2020-02-01 00:00:05.000')
@@ -583,7 +582,7 @@ class TDTestCase:
 
         # multiple _irowts
         tdSql.query(f"select interp(c0),_irowts from {dbname}.{tbname} range('2020-02-01 00:00:04', '2020-02-01 00:00:16') every(1s) fill(linear)")
-        tdSql.checkRows(12)
+        tdSql.checkRows(11)
         tdSql.checkCols(2)
 
         tdSql.checkData(0, 1, '2020-02-01 00:00:05.000')
@@ -599,7 +598,7 @@ class TDTestCase:
         tdSql.checkData(10, 1, '2020-02-01 00:00:15.000')
 
         tdSql.query(f"select _irowts, interp(c0), interp(c0), _irowts from {dbname}.{tbname} range('2020-02-01 00:00:04', '2020-02-01 00:00:16') every(1s) fill(linear)")
-        tdSql.checkRows(12)
+        tdSql.checkRows(11)
         tdSql.checkCols(4)
 
         cols = (0, 3)
@@ -837,7 +836,944 @@ class TDTestCase:
         tdSql.checkData(0, 0, 15)
         tdSql.checkData(1, 0, 15)
 
-        tdLog.printNoPrefix("==========step10:test multi-interp cases")
+        # test fill linear
+
+        ## | {. | | .} |
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:05', '2020-02-11 00:00:05') every(1d) fill(linear)")
+        tdSql.checkRows(11)
+        tdSql.checkData(0, 0, 5)
+        tdSql.checkData(1, 0, 6)
+        tdSql.checkData(2, 0, 7)
+        tdSql.checkData(3, 0, 8)
+        tdSql.checkData(4, 0, 9)
+        tdSql.checkData(5, 0, 10)
+        tdSql.checkData(6, 0, 11)
+        tdSql.checkData(7, 0, 12)
+        tdSql.checkData(8, 0, 13)
+        tdSql.checkData(9, 0, 14)
+        tdSql.checkData(10, 0, 15)
+
+        ## | . | {} | . |
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname} range('2020-02-03 00:00:05', '2020-02-07 00:00:05') every(1d) fill(linear)")
+        tdSql.checkRows(5)
+        tdSql.checkData(0, 0, 7)
+        tdSql.checkData(1, 0, 8)
+        tdSql.checkData(2, 0, 9)
+        tdSql.checkData(3, 0, 10)
+        tdSql.checkData(4, 0, 11)
+
+        ## | {. | } | . |
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname} range('2020-01-31 00:00:05', '2020-02-05 00:00:05') every(1d) fill(linear)")
+        tdSql.checkRows(5)
+        tdSql.checkData(0, 0, 5)
+        tdSql.checkData(1, 0, 6)
+        tdSql.checkData(2, 0, 7)
+        tdSql.checkData(3, 0, 8)
+        tdSql.checkData(4, 0, 9)
+
+        ## | . | { | .} |
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname} range('2020-02-10 00:00:05', '2020-02-15 00:00:05') every(1d) fill(linear)")
+        tdSql.checkRows(2)
+        tdSql.checkData(0, 0, 14)
+        tdSql.checkData(1, 0, 15)
+
+
+        tdLog.printNoPrefix("==========step10:test interp with null data")
+        tdSql.execute(
+            f'''create table if not exists {dbname}.{tbname1}
+            (ts timestamp, c0 int, c1 int)
+            '''
+        )
+
+
+        tdSql.execute(f"insert into {dbname}.{tbname1} values ('2020-02-02 00:00:00', 0,    NULL)")
+        tdSql.execute(f"insert into {dbname}.{tbname1} values ('2020-02-02 00:00:05', NULL, NULL)")
+        tdSql.execute(f"insert into {dbname}.{tbname1} values ('2020-02-02 00:00:10', 10,   10)")
+        tdSql.execute(f"insert into {dbname}.{tbname1} values ('2020-02-02 00:00:15', NULL, NULL)")
+        tdSql.execute(f"insert into {dbname}.{tbname1} values ('2020-02-02 00:00:20', 20,   NULL)")
+        tdSql.execute(f"insert into {dbname}.{tbname1} values ('2020-02-02 00:00:25', NULL, NULL)")
+        tdSql.execute(f"insert into {dbname}.{tbname1} values ('2020-02-02 00:00:30', 30,   30)")
+        tdSql.execute(f"insert into {dbname}.{tbname1} values ('2020-02-02 00:00:35', 35,   NULL)")
+        tdSql.execute(f"insert into {dbname}.{tbname1} values ('2020-02-02 00:00:40', 40,   40)")
+        tdSql.execute(f"insert into {dbname}.{tbname1} values ('2020-02-02 00:00:45', NULL, 45)")
+        tdSql.execute(f"insert into {dbname}.{tbname1} values ('2020-02-02 00:00:50', 50,   NULL)")
+        tdSql.execute(f"insert into {dbname}.{tbname1} values ('2020-02-02 00:00:55', NULL, NULL)")
+        tdSql.execute(f"insert into {dbname}.{tbname1} values ('2020-02-02 00:01:00', 55,   60)")
+
+        # test fill linear
+
+        # check c0
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-01 23:59:59', '2020-02-02 00:00:00') every(1s) fill(linear)")
+        tdSql.checkRows(1)
+        tdSql.checkData(0, 0, 0)
+
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-01 23:59:59', '2020-02-02 00:00:03') every(1s) fill(linear)")
+        tdSql.checkRows(4)
+        tdSql.checkData(0, 0, 0)
+        tdSql.checkData(1, 0, None)
+        tdSql.checkData(2, 0, None)
+        tdSql.checkData(3, 0, None)
+
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-01 23:59:59', '2020-02-02 00:00:05') every(1s) fill(linear)")
+        tdSql.checkRows(6)
+        tdSql.checkData(0, 0, 0)
+        tdSql.checkData(1, 0, None)
+        tdSql.checkData(2, 0, None)
+        tdSql.checkData(3, 0, None)
+        tdSql.checkData(4, 0, None)
+        tdSql.checkData(5, 0, None)
+
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-01 23:59:59', '2020-02-02 00:00:08') every(1s) fill(linear)")
+        tdSql.checkRows(9)
+        tdSql.checkData(0, 0, 0)
+        tdSql.checkData(1, 0, None)
+        tdSql.checkData(2, 0, None)
+        tdSql.checkData(3, 0, None)
+        tdSql.checkData(4, 0, None)
+        tdSql.checkData(5, 0, None)
+        tdSql.checkData(6, 0, None)
+        tdSql.checkData(7, 0, None)
+        tdSql.checkData(8, 0, None)
+
+
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-02 00:00:01', '2020-02-02 00:00:03') every(1s) fill(linear)")
+        tdSql.checkRows(3)
+        tdSql.checkData(0, 0, None)
+        tdSql.checkData(1, 0, None)
+        tdSql.checkData(2, 0, None)
+
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-02 00:00:03', '2020-02-02 00:00:08') every(1s) fill(linear)")
+        tdSql.checkRows(6)
+        tdSql.checkData(0, 0, None)
+        tdSql.checkData(1, 0, None)
+        tdSql.checkData(2, 0, None)
+        tdSql.checkData(3, 0, None)
+        tdSql.checkData(4, 0, None)
+        tdSql.checkData(5, 0, None)
+
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-02 00:00:05', '2020-02-02 00:00:10') every(1s) fill(linear)")
+        tdSql.checkRows(6)
+        tdSql.checkData(0, 0, None)
+        tdSql.checkData(1, 0, None)
+        tdSql.checkData(2, 0, None)
+        tdSql.checkData(3, 0, None)
+        tdSql.checkData(4, 0, None)
+        tdSql.checkData(5, 0, 10)
+
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-02 00:00:05', '2020-02-02 00:00:15') every(1s) fill(linear)")
+        tdSql.checkRows(11)
+        tdSql.checkData(0,  0, None)
+        tdSql.checkData(1,  0, None)
+        tdSql.checkData(2,  0, None)
+        tdSql.checkData(3,  0, None)
+        tdSql.checkData(4,  0, None)
+        tdSql.checkData(5,  0, 10)
+        tdSql.checkData(6,  0, None)
+        tdSql.checkData(7,  0, None)
+        tdSql.checkData(8,  0, None)
+        tdSql.checkData(9,  0, None)
+        tdSql.checkData(10, 0, None)
+
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-02 00:00:05', '2020-02-02 00:00:18') every(1s) fill(linear)")
+        tdSql.checkRows(14)
+        tdSql.checkData(0,  0, None)
+        tdSql.checkData(1,  0, None)
+        tdSql.checkData(2,  0, None)
+        tdSql.checkData(3,  0, None)
+        tdSql.checkData(4,  0, None)
+        tdSql.checkData(5,  0, 10)
+        tdSql.checkData(6,  0, None)
+        tdSql.checkData(7,  0, None)
+        tdSql.checkData(8,  0, None)
+        tdSql.checkData(9,  0, None)
+        tdSql.checkData(10, 0, None)
+        tdSql.checkData(11, 0, None)
+        tdSql.checkData(12, 0, None)
+        tdSql.checkData(13, 0, None)
+
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-02 00:00:05', '2020-02-02 00:00:20') every(1s) fill(linear)")
+        tdSql.checkRows(16)
+        tdSql.checkData(0,  0, None)
+        tdSql.checkData(1,  0, None)
+        tdSql.checkData(2,  0, None)
+        tdSql.checkData(3,  0, None)
+        tdSql.checkData(4,  0, None)
+        tdSql.checkData(5,  0, 10)
+        tdSql.checkData(6,  0, None)
+        tdSql.checkData(7,  0, None)
+        tdSql.checkData(8,  0, None)
+        tdSql.checkData(9,  0, None)
+        tdSql.checkData(10, 0, None)
+        tdSql.checkData(11, 0, None)
+        tdSql.checkData(12, 0, None)
+        tdSql.checkData(13, 0, None)
+        tdSql.checkData(14, 0, None)
+        tdSql.checkData(15, 0, 20)
+
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-02 00:00:09', '2020-02-02 00:00:11') every(1s) fill(linear)")
+        tdSql.checkRows(3)
+        tdSql.checkData(0, 0, None)
+        tdSql.checkData(1, 0, 10)
+        tdSql.checkData(2, 0, None)
+
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-02 00:00:10', '2020-02-02 00:00:15') every(1s) fill(linear)")
+        tdSql.checkRows(6)
+        tdSql.checkData(0, 0, 10)
+        tdSql.checkData(1, 0, None)
+        tdSql.checkData(2, 0, None)
+        tdSql.checkData(3, 0, None)
+        tdSql.checkData(4, 0, None)
+        tdSql.checkData(5, 0, None)
+
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-02 00:00:12', '2020-02-02 00:00:13') every(1s) fill(linear)")
+        tdSql.checkRows(2)
+        tdSql.checkData(0, 0, None)
+        tdSql.checkData(1, 0, None)
+
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-02 00:00:12', '2020-02-02 00:00:15') every(1s) fill(linear)")
+        tdSql.checkRows(4)
+        tdSql.checkData(0, 0, None)
+        tdSql.checkData(1, 0, None)
+        tdSql.checkData(2, 0, None)
+        tdSql.checkData(3, 0, None)
+
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-02 00:00:12', '2020-02-02 00:00:18') every(1s) fill(linear)")
+        tdSql.checkRows(7)
+        tdSql.checkData(0,  0, None)
+        tdSql.checkData(1,  0, None)
+        tdSql.checkData(2,  0, None)
+        tdSql.checkData(3,  0, None)
+        tdSql.checkData(4,  0, None)
+        tdSql.checkData(5,  0, None)
+        tdSql.checkData(6,  0, None)
+
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-02 00:00:30', '2020-02-02 00:00:40') every(1s) fill(linear)")
+        tdSql.checkRows(11)
+        tdSql.checkData(0,  0, 30)
+        tdSql.checkData(1,  0, 31)
+        tdSql.checkData(2,  0, 32)
+        tdSql.checkData(3,  0, 33)
+        tdSql.checkData(4,  0, 34)
+        tdSql.checkData(5,  0, 35)
+        tdSql.checkData(6,  0, 36)
+        tdSql.checkData(7,  0, 37)
+        tdSql.checkData(8,  0, 38)
+        tdSql.checkData(9,  0, 39)
+        tdSql.checkData(10, 0, 40)
+
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-02 00:00:25', '2020-02-02 00:00:45') every(1s) fill(linear)")
+        tdSql.checkRows(21)
+        tdSql.checkData(5,  0, 30)
+        tdSql.checkData(6,  0, 31)
+        tdSql.checkData(7,  0, 32)
+        tdSql.checkData(8,  0, 33)
+        tdSql.checkData(9,  0, 34)
+        tdSql.checkData(10, 0, 35)
+        tdSql.checkData(11, 0, 36)
+        tdSql.checkData(12, 0, 37)
+        tdSql.checkData(13, 0, 38)
+        tdSql.checkData(14, 0, 39)
+        tdSql.checkData(15, 0, 40)
+
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-02 00:00:20', '2020-02-02 00:00:40') every(1s) fill(linear)")
+        tdSql.checkRows(21)
+        tdSql.checkData(0,  0, 20)
+        tdSql.checkData(10, 0, 30)
+        tdSql.checkData(11, 0, 31)
+        tdSql.checkData(12, 0, 32)
+        tdSql.checkData(13, 0, 33)
+        tdSql.checkData(14, 0, 34)
+        tdSql.checkData(15, 0, 35)
+        tdSql.checkData(16, 0, 36)
+        tdSql.checkData(17, 0, 37)
+        tdSql.checkData(18, 0, 38)
+        tdSql.checkData(19, 0, 39)
+        tdSql.checkData(20, 0, 40)
+
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-02 00:00:30', '2020-02-02 00:00:50') every(1s) fill(linear)")
+        tdSql.checkRows(21)
+        tdSql.checkData(0,  0, 30)
+        tdSql.checkData(1,  0, 31)
+        tdSql.checkData(2,  0, 32)
+        tdSql.checkData(3,  0, 33)
+        tdSql.checkData(4,  0, 34)
+        tdSql.checkData(5,  0, 35)
+        tdSql.checkData(6,  0, 36)
+        tdSql.checkData(7,  0, 37)
+        tdSql.checkData(8,  0, 38)
+        tdSql.checkData(9,  0, 39)
+        tdSql.checkData(10, 0, 40)
+        tdSql.checkData(20, 0, 50)
+
+        tdSql.query(f"select interp(c0) from {dbname}.{tbname1} range('2020-02-02 00:00:20', '2020-02-02 00:00:50') every(1s) fill(linear)")
+        tdSql.checkRows(31)
+        tdSql.checkData(0,  0, 20)
+        tdSql.checkData(10, 0, 30)
+        tdSql.checkData(11, 0, 31)
+        tdSql.checkData(12, 0, 32)
+        tdSql.checkData(13, 0, 33)
+        tdSql.checkData(14, 0, 34)
+        tdSql.checkData(15, 0, 35)
+        tdSql.checkData(16, 0, 36)
+        tdSql.checkData(17, 0, 37)
+        tdSql.checkData(18, 0, 38)
+        tdSql.checkData(19, 0, 39)
+        tdSql.checkData(20, 0, 40)
+        tdSql.checkData(30, 0, 50)
+
+        # check c1
+        tdSql.query(f"select interp(c1) from {dbname}.{tbname1} range('2020-02-01 23:59:59', '2020-02-02 00:00:05') every(1s) fill(linear)")
+        tdSql.checkRows(6)
+        tdSql.checkData(0,  0, None)
+        tdSql.checkData(1,  0, None)
+        tdSql.checkData(2,  0, None)
+        tdSql.checkData(3,  0, None)
+        tdSql.checkData(4,  0, None)
+        tdSql.checkData(5,  0, None)
+
+        tdSql.query(f"select interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:00', '2020-02-02 00:00:05') every(1s) fill(linear)")
+        tdSql.checkRows(6)
+        tdSql.checkData(0,  0, None)
+        tdSql.checkData(1,  0, None)
+        tdSql.checkData(2,  0, None)
+        tdSql.checkData(3,  0, None)
+        tdSql.checkData(4,  0, None)
+        tdSql.checkData(5,  0, None)
+
+        tdSql.query(f"select interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:00', '2020-02-02 00:00:08') every(1s) fill(linear)")
+        tdSql.checkRows(9)
+        tdSql.checkData(0,  0, None)
+        tdSql.checkData(1,  0, None)
+        tdSql.checkData(2,  0, None)
+        tdSql.checkData(3,  0, None)
+        tdSql.checkData(4,  0, None)
+        tdSql.checkData(5,  0, None)
+        tdSql.checkData(6,  0, None)
+        tdSql.checkData(7,  0, None)
+        tdSql.checkData(8,  0, None)
+
+        tdSql.query(f"select interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:00', '2020-02-02 00:00:10') every(1s) fill(linear)")
+        tdSql.checkRows(11)
+        tdSql.checkData(0,  0, None)
+        tdSql.checkData(1,  0, None)
+        tdSql.checkData(2,  0, None)
+        tdSql.checkData(3,  0, None)
+        tdSql.checkData(4,  0, None)
+        tdSql.checkData(5,  0, None)
+        tdSql.checkData(6,  0, None)
+        tdSql.checkData(7,  0, None)
+        tdSql.checkData(8,  0, None)
+        tdSql.checkData(9,  0, None)
+        tdSql.checkData(10, 0, 10)
+
+        tdSql.query(f"select interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:00', '2020-02-02 00:00:15') every(1s) fill(linear)")
+        tdSql.checkRows(16)
+        tdSql.checkData(0,  0, None)
+        tdSql.checkData(1,  0, None)
+        tdSql.checkData(2,  0, None)
+        tdSql.checkData(3,  0, None)
+        tdSql.checkData(4,  0, None)
+        tdSql.checkData(5,  0, None)
+        tdSql.checkData(6,  0, None)
+        tdSql.checkData(7,  0, None)
+        tdSql.checkData(8,  0, None)
+        tdSql.checkData(9,  0, None)
+        tdSql.checkData(10, 0, 10)
+        tdSql.checkData(11,  0, None)
+        tdSql.checkData(12,  0, None)
+        tdSql.checkData(13,  0, None)
+        tdSql.checkData(14,  0, None)
+        tdSql.checkData(15,  0, None)
+
+        tdSql.query(f"select interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:00', '2020-02-02 00:00:20') every(1s) fill(linear)")
+        tdSql.checkRows(21)
+        tdSql.checkData(0,  0, None)
+        tdSql.checkData(1,  0, None)
+        tdSql.checkData(2,  0, None)
+        tdSql.checkData(3,  0, None)
+        tdSql.checkData(4,  0, None)
+        tdSql.checkData(5,  0, None)
+        tdSql.checkData(6,  0, None)
+        tdSql.checkData(7,  0, None)
+        tdSql.checkData(8,  0, None)
+        tdSql.checkData(9,  0, None)
+        tdSql.checkData(10, 0, 10)
+        tdSql.checkData(11,  0, None)
+        tdSql.checkData(12,  0, None)
+        tdSql.checkData(13,  0, None)
+        tdSql.checkData(14,  0, None)
+        tdSql.checkData(15,  0, None)
+        tdSql.checkData(16,  0, None)
+        tdSql.checkData(17,  0, None)
+        tdSql.checkData(18,  0, None)
+        tdSql.checkData(19,  0, None)
+        tdSql.checkData(20,  0, None)
+
+        tdSql.query(f"select interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:00', '2020-02-02 00:00:25') every(1s) fill(linear)")
+        tdSql.checkRows(26)
+        tdSql.checkData(0,  0, None)
+        tdSql.checkData(1,  0, None)
+        tdSql.checkData(2,  0, None)
+        tdSql.checkData(3,  0, None)
+        tdSql.checkData(4,  0, None)
+        tdSql.checkData(5,  0, None)
+        tdSql.checkData(6,  0, None)
+        tdSql.checkData(7,  0, None)
+        tdSql.checkData(8,  0, None)
+        tdSql.checkData(9,  0, None)
+        tdSql.checkData(10, 0, 10)
+        tdSql.checkData(11,  0, None)
+        tdSql.checkData(12,  0, None)
+        tdSql.checkData(13,  0, None)
+        tdSql.checkData(14,  0, None)
+        tdSql.checkData(15,  0, None)
+        tdSql.checkData(16,  0, None)
+        tdSql.checkData(17,  0, None)
+        tdSql.checkData(18,  0, None)
+        tdSql.checkData(19,  0, None)
+        tdSql.checkData(20,  0, None)
+        tdSql.checkData(21,  0, None)
+        tdSql.checkData(22,  0, None)
+        tdSql.checkData(23,  0, None)
+        tdSql.checkData(24,  0, None)
+        tdSql.checkData(25,  0, None)
+
+        tdSql.query(f"select interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:00', '2020-02-02 00:00:30') every(1s) fill(linear)")
+        tdSql.checkRows(31)
+        tdSql.checkData(0,  0, None)
+        tdSql.checkData(1,  0, None)
+        tdSql.checkData(2,  0, None)
+        tdSql.checkData(3,  0, None)
+        tdSql.checkData(4,  0, None)
+        tdSql.checkData(5,  0, None)
+        tdSql.checkData(6,  0, None)
+        tdSql.checkData(7,  0, None)
+        tdSql.checkData(8,  0, None)
+        tdSql.checkData(9,  0, None)
+        tdSql.checkData(10, 0, 10)
+        tdSql.checkData(11,  0, None)
+        tdSql.checkData(12,  0, None)
+        tdSql.checkData(13,  0, None)
+        tdSql.checkData(14,  0, None)
+        tdSql.checkData(15,  0, None)
+        tdSql.checkData(16,  0, None)
+        tdSql.checkData(17,  0, None)
+        tdSql.checkData(18,  0, None)
+        tdSql.checkData(19,  0, None)
+        tdSql.checkData(20,  0, None)
+        tdSql.checkData(21,  0, None)
+        tdSql.checkData(22,  0, None)
+        tdSql.checkData(23,  0, None)
+        tdSql.checkData(24,  0, None)
+        tdSql.checkData(25,  0, None)
+        tdSql.checkData(26,  0, None)
+        tdSql.checkData(27,  0, None)
+        tdSql.checkData(28,  0, None)
+        tdSql.checkData(29,  0, None)
+        tdSql.checkData(30,  0, 30)
+
+        tdSql.query(f"select interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:00', '2020-02-02 00:00:35') every(1s) fill(linear)")
+        tdSql.checkRows(36)
+        tdSql.checkData(10, 0, 10)
+        tdSql.checkData(30, 0, 30)
+
+        tdSql.query(f"select interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:00', '2020-02-02 00:00:40') every(1s) fill(linear)")
+        tdSql.checkRows(41)
+        tdSql.checkData(10, 0, 10)
+        tdSql.checkData(30, 0, 30)
+        tdSql.checkData(40, 0, 40)
+
+        tdSql.query(f"select interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:00', '2020-02-02 00:00:45') every(1s) fill(linear)")
+        tdSql.checkRows(46)
+        tdSql.checkData(10, 0, 10)
+        tdSql.checkData(30, 0, 30)
+        tdSql.checkData(40, 0, 40)
+        tdSql.checkData(41, 0, 41)
+        tdSql.checkData(42, 0, 42)
+        tdSql.checkData(43, 0, 43)
+        tdSql.checkData(44, 0, 44)
+        tdSql.checkData(45, 0, 45)
+
+        tdSql.query(f"select interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:00', '2020-02-02 00:00:50') every(1s) fill(linear)")
+        tdSql.checkRows(51)
+        tdSql.checkData(10, 0, 10)
+        tdSql.checkData(30, 0, 30)
+        tdSql.checkData(40, 0, 40)
+        tdSql.checkData(41, 0, 41)
+        tdSql.checkData(42, 0, 42)
+        tdSql.checkData(43, 0, 43)
+        tdSql.checkData(44, 0, 44)
+        tdSql.checkData(45, 0, 45)
+
+
+        tdSql.query(f"select interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:00', '2020-02-02 00:00:55') every(1s) fill(linear)")
+        tdSql.checkRows(56)
+        tdSql.checkData(10, 0, 10)
+        tdSql.checkData(30, 0, 30)
+        tdSql.checkData(40, 0, 40)
+        tdSql.checkData(41, 0, 41)
+        tdSql.checkData(42, 0, 42)
+        tdSql.checkData(43, 0, 43)
+        tdSql.checkData(44, 0, 44)
+        tdSql.checkData(45, 0, 45)
+
+
+        tdSql.query(f"select interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:00', '2020-02-02 00:01:00') every(1s) fill(linear)")
+        tdSql.checkRows(61)
+        tdSql.checkData(10, 0, 10)
+        tdSql.checkData(30, 0, 30)
+        tdSql.checkData(40, 0, 40)
+        tdSql.checkData(41, 0, 41)
+        tdSql.checkData(42, 0, 42)
+        tdSql.checkData(43, 0, 43)
+        tdSql.checkData(44, 0, 44)
+        tdSql.checkData(45, 0, 45)
+        tdSql.checkData(60, 0, 60)
+
+        tdSql.query(f"select interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:40', '2020-02-02 00:00:45') every(1s) fill(linear)")
+        tdSql.checkRows(6)
+        tdSql.checkData(0, 0, 40)
+        tdSql.checkData(1, 0, 41)
+        tdSql.checkData(2, 0, 42)
+        tdSql.checkData(3, 0, 43)
+        tdSql.checkData(4, 0, 44)
+        tdSql.checkData(5, 0, 45)
+
+        tdSql.query(f"select interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:35', '2020-02-02 00:00:50') every(1s) fill(linear)")
+        tdSql.checkRows(16)
+        tdSql.checkData(5,  0, 40)
+        tdSql.checkData(6,  0, 41)
+        tdSql.checkData(7,  0, 42)
+        tdSql.checkData(8,  0, 43)
+        tdSql.checkData(9,  0, 44)
+        tdSql.checkData(10, 0, 45)
+
+        tdSql.query(f"select interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:35', '2020-02-02 00:00:55') every(1s) fill(linear)")
+        tdSql.checkRows(21)
+        tdSql.checkData(5,  0, 40)
+        tdSql.checkData(6,  0, 41)
+        tdSql.checkData(7,  0, 42)
+        tdSql.checkData(8,  0, 43)
+        tdSql.checkData(9,  0, 44)
+        tdSql.checkData(10, 0, 45)
+
+        tdSql.query(f"select interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:30', '2020-02-02 00:01:00') every(1s) fill(linear)")
+        tdSql.checkRows(31)
+        tdSql.checkData(0,  0, 30)
+        tdSql.checkData(10, 0, 40)
+        tdSql.checkData(11, 0, 41)
+        tdSql.checkData(12, 0, 42)
+        tdSql.checkData(13, 0, 43)
+        tdSql.checkData(14, 0, 44)
+        tdSql.checkData(15, 0, 45)
+        tdSql.checkData(30, 0, 60)
+
+        # two interps
+        tdSql.query(f"select interp(c0),interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:00', '2020-02-02 00:01:00') every(1s) fill(linear)")
+        tdSql.checkRows(61)
+        tdSql.checkCols(2)
+        tdSql.checkData(0,  0, 0)    #
+        tdSql.checkData(1,  0, None)
+        tdSql.checkData(4,  0, None)
+        tdSql.checkData(5,  0, None) #
+        tdSql.checkData(6,  0, None)
+        tdSql.checkData(9,  0, None)
+        tdSql.checkData(10, 0, 10)   #
+        tdSql.checkData(11, 0, None)
+        tdSql.checkData(14, 0, None)
+        tdSql.checkData(15, 0, None) #
+        tdSql.checkData(16, 0, None)
+        tdSql.checkData(19, 0, None)
+        tdSql.checkData(20, 0, 20)   #
+        tdSql.checkData(21, 0, None)
+        tdSql.checkData(24, 0, None)
+        tdSql.checkData(25, 0, None) #
+        tdSql.checkData(26, 0, None)
+        tdSql.checkData(29, 0, None)
+        tdSql.checkData(30, 0, 30)   #
+        tdSql.checkData(31, 0, 31)
+        tdSql.checkData(32, 0, 32)
+        tdSql.checkData(33, 0, 33)
+        tdSql.checkData(34, 0, 34)
+        tdSql.checkData(35, 0, 35)   #
+        tdSql.checkData(36, 0, 36)
+        tdSql.checkData(37, 0, 37)
+        tdSql.checkData(38, 0, 38)
+        tdSql.checkData(39, 0, 39)
+        tdSql.checkData(40, 0, 40)   #
+        tdSql.checkData(41, 0, None)
+        tdSql.checkData(44, 0, None)
+        tdSql.checkData(45, 0, None) #
+        tdSql.checkData(46, 0, None)
+        tdSql.checkData(49, 0, None)
+        tdSql.checkData(50, 0, 50)   #
+        tdSql.checkData(51, 0, None)
+        tdSql.checkData(54, 0, None)
+        tdSql.checkData(55, 0, None) #
+        tdSql.checkData(56, 0, None)
+        tdSql.checkData(59, 0, None)
+        tdSql.checkData(60, 0, 55)   #
+
+        tdSql.checkData(0,  1, None) #
+        tdSql.checkData(1,  1, None)
+        tdSql.checkData(4,  1, None)
+        tdSql.checkData(5,  1, None) #
+        tdSql.checkData(6,  1, None)
+        tdSql.checkData(9,  1, None)
+        tdSql.checkData(10, 1, 10)   #
+        tdSql.checkData(11, 1, None)
+        tdSql.checkData(14, 1, None)
+        tdSql.checkData(15, 1, None) #
+        tdSql.checkData(16, 1, None)
+        tdSql.checkData(19, 1, None)
+        tdSql.checkData(20, 1, None) #
+        tdSql.checkData(21, 1, None)
+        tdSql.checkData(24, 1, None)
+        tdSql.checkData(25, 1, None) #
+        tdSql.checkData(26, 1, None)
+        tdSql.checkData(29, 1, None)
+        tdSql.checkData(30, 1, 30)   #
+        tdSql.checkData(31, 1, None)
+        tdSql.checkData(34, 1, None)
+        tdSql.checkData(35, 1, None) #
+        tdSql.checkData(36, 1, None)
+        tdSql.checkData(39, 1, None)
+        tdSql.checkData(40, 1, 40)   #
+        tdSql.checkData(41, 1, 41)
+        tdSql.checkData(42, 1, 42)
+        tdSql.checkData(43, 1, 43)
+        tdSql.checkData(44, 1, 44)
+        tdSql.checkData(45, 1, 45)   #
+        tdSql.checkData(46, 1, None)
+        tdSql.checkData(49, 1, None)
+        tdSql.checkData(50, 1, None) #
+        tdSql.checkData(51, 1, None)
+        tdSql.checkData(54, 1, None)
+        tdSql.checkData(55, 1, None) #
+        tdSql.checkData(56, 1, None)
+        tdSql.checkData(59, 1, None)
+        tdSql.checkData(60, 1, 60)   #
+
+        # test fill null
+        tdSql.query(f"select interp(c0),interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:00', '2020-02-02 00:01:00') every(1s) fill(null)")
+        tdSql.checkRows(61)
+        tdSql.checkCols(2)
+        tdSql.checkData(0,  0, 0)    #
+        tdSql.checkData(1,  0, None)
+        tdSql.checkData(4,  0, None)
+        tdSql.checkData(5,  0, None) #
+        tdSql.checkData(6,  0, None)
+        tdSql.checkData(9,  0, None)
+        tdSql.checkData(10, 0, 10)   #
+        tdSql.checkData(11, 0, None)
+        tdSql.checkData(14, 0, None)
+        tdSql.checkData(15, 0, None) #
+        tdSql.checkData(16, 0, None)
+        tdSql.checkData(19, 0, None)
+        tdSql.checkData(20, 0, 20)   #
+        tdSql.checkData(21, 0, None)
+        tdSql.checkData(24, 0, None)
+        tdSql.checkData(25, 0, None) #
+        tdSql.checkData(26, 0, None)
+        tdSql.checkData(29, 0, None)
+        tdSql.checkData(30, 0, 30)   #
+        tdSql.checkData(31, 0, None)
+        tdSql.checkData(34, 0, None)
+        tdSql.checkData(35, 0, 35)   #
+        tdSql.checkData(36, 0, None)
+        tdSql.checkData(39, 0, None)
+        tdSql.checkData(40, 0, 40)   #
+        tdSql.checkData(41, 0, None)
+        tdSql.checkData(44, 0, None)
+        tdSql.checkData(45, 0, None) #
+        tdSql.checkData(46, 0, None)
+        tdSql.checkData(49, 0, None)
+        tdSql.checkData(50, 0, 50)   #
+        tdSql.checkData(51, 0, None)
+        tdSql.checkData(54, 0, None)
+        tdSql.checkData(55, 0, None) #
+        tdSql.checkData(56, 0, None)
+        tdSql.checkData(59, 0, None)
+        tdSql.checkData(60, 0, 55)   #
+
+        tdSql.checkData(0,  1, None) #
+        tdSql.checkData(1,  1, None)
+        tdSql.checkData(4,  1, None)
+        tdSql.checkData(5,  1, None) #
+        tdSql.checkData(6,  1, None)
+        tdSql.checkData(9,  1, None)
+        tdSql.checkData(10, 1, 10)   #
+        tdSql.checkData(11, 1, None)
+        tdSql.checkData(14, 1, None)
+        tdSql.checkData(15, 1, None) #
+        tdSql.checkData(16, 1, None)
+        tdSql.checkData(19, 1, None)
+        tdSql.checkData(20, 1, None) #
+        tdSql.checkData(21, 1, None)
+        tdSql.checkData(24, 1, None)
+        tdSql.checkData(25, 1, None) #
+        tdSql.checkData(26, 1, None)
+        tdSql.checkData(29, 1, None)
+        tdSql.checkData(30, 1, 30)   #
+        tdSql.checkData(31, 1, None)
+        tdSql.checkData(34, 1, None)
+        tdSql.checkData(35, 1, None) #
+        tdSql.checkData(36, 1, None)
+        tdSql.checkData(39, 1, None)
+        tdSql.checkData(40, 1, 40)   #
+        tdSql.checkData(41, 1, None)
+        tdSql.checkData(44, 1, None)
+        tdSql.checkData(45, 1, 45)   #
+        tdSql.checkData(46, 1, None)
+        tdSql.checkData(49, 1, None)
+        tdSql.checkData(50, 1, None) #
+        tdSql.checkData(51, 1, None)
+        tdSql.checkData(54, 1, None)
+        tdSql.checkData(55, 1, None) #
+        tdSql.checkData(56, 1, None)
+        tdSql.checkData(59, 1, None)
+        tdSql.checkData(60, 1, 60)   #
+
+        # test fill value
+        tdSql.query(f"select interp(c0),interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:00', '2020-02-02 00:01:00') every(1s) fill(value, 123)")
+        tdSql.checkRows(61)
+        tdSql.checkCols(2)
+        tdSql.checkData(0,  0, 0)    #
+        tdSql.checkData(1,  0, 123)
+        tdSql.checkData(4,  0, 123)
+        tdSql.checkData(5,  0, None) #
+        tdSql.checkData(6,  0, 123)
+        tdSql.checkData(9,  0, 123)
+        tdSql.checkData(10, 0, 10)   #
+        tdSql.checkData(11, 0, 123)
+        tdSql.checkData(14, 0, 123)
+        tdSql.checkData(15, 0, None) #
+        tdSql.checkData(16, 0, 123)
+        tdSql.checkData(19, 0, 123)
+        tdSql.checkData(20, 0, 20)   #
+        tdSql.checkData(21, 0, 123)
+        tdSql.checkData(24, 0, 123)
+        tdSql.checkData(25, 0, None) #
+        tdSql.checkData(26, 0, 123)
+        tdSql.checkData(29, 0, 123)
+        tdSql.checkData(30, 0, 30)   #
+        tdSql.checkData(31, 0, 123)
+        tdSql.checkData(34, 0, 123)
+        tdSql.checkData(35, 0, 35)   #
+        tdSql.checkData(36, 0, 123)
+        tdSql.checkData(39, 0, 123)
+        tdSql.checkData(40, 0, 40)   #
+        tdSql.checkData(41, 0, 123)
+        tdSql.checkData(44, 0, 123)
+        tdSql.checkData(45, 0, None) #
+        tdSql.checkData(46, 0, 123)
+        tdSql.checkData(49, 0, 123)
+        tdSql.checkData(50, 0, 50)   #
+        tdSql.checkData(51, 0, 123)
+        tdSql.checkData(54, 0, 123)
+        tdSql.checkData(55, 0, None) #
+        tdSql.checkData(59, 0, 123)
+        tdSql.checkData(60, 0, 55)   #
+
+        tdSql.checkData(0,  1, None) #
+        tdSql.checkData(1,  1, 123)
+        tdSql.checkData(4,  1, 123)
+        tdSql.checkData(5,  1, None) #
+        tdSql.checkData(6,  1, 123)
+        tdSql.checkData(9,  1, 123)
+        tdSql.checkData(10, 1, 10)   #
+        tdSql.checkData(11, 1, 123)
+        tdSql.checkData(14, 1, 123)
+        tdSql.checkData(15, 1, None) #
+        tdSql.checkData(16, 1, 123)
+        tdSql.checkData(19, 1, 123)
+        tdSql.checkData(20, 1, None) #
+        tdSql.checkData(21, 1, 123)
+        tdSql.checkData(24, 1, 123)
+        tdSql.checkData(25, 1, None) #
+        tdSql.checkData(26, 1, 123)
+        tdSql.checkData(29, 1, 123)
+        tdSql.checkData(30, 1, 30)   #
+        tdSql.checkData(31, 1, 123)
+        tdSql.checkData(34, 1, 123)
+        tdSql.checkData(35, 1, None) #
+        tdSql.checkData(36, 1, 123)
+        tdSql.checkData(39, 1, 123)
+        tdSql.checkData(40, 1, 40)   #
+        tdSql.checkData(41, 1, 123)
+        tdSql.checkData(44, 1, 123)
+        tdSql.checkData(45, 1, 45)   #
+        tdSql.checkData(46, 1, 123)
+        tdSql.checkData(49, 1, 123)
+        tdSql.checkData(50, 1, None) #
+        tdSql.checkData(51, 1, 123)
+        tdSql.checkData(54, 1, 123)
+        tdSql.checkData(55, 1, None) #
+        tdSql.checkData(56, 1, 123)
+        tdSql.checkData(59, 1, 123)
+        tdSql.checkData(60, 1, 60)   #
+
+        # test fill prev
+        tdSql.query(f"select interp(c0),interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:00', '2020-02-02 00:01:00') every(1s) fill(prev)")
+        tdSql.checkRows(61)
+        tdSql.checkCols(2)
+        tdSql.checkData(0,  0, 0)    #
+        tdSql.checkData(1,  0, 0)
+        tdSql.checkData(4,  0, 0)
+        tdSql.checkData(5,  0, None) #
+        tdSql.checkData(6,  0, None)
+        tdSql.checkData(9,  0, None)
+        tdSql.checkData(10, 0, 10)   #
+        tdSql.checkData(11, 0, 10)
+        tdSql.checkData(14, 0, 10)
+        tdSql.checkData(15, 0, None) #
+        tdSql.checkData(16, 0, None)
+        tdSql.checkData(19, 0, None)
+        tdSql.checkData(20, 0, 20)   #
+        tdSql.checkData(21, 0, 20)
+        tdSql.checkData(24, 0, 20)
+        tdSql.checkData(25, 0, None) #
+        tdSql.checkData(26, 0, None)
+        tdSql.checkData(29, 0, None)
+        tdSql.checkData(30, 0, 30)   #
+        tdSql.checkData(31, 0, 30)
+        tdSql.checkData(34, 0, 30)
+        tdSql.checkData(35, 0, 35)   #
+        tdSql.checkData(36, 0, 35)
+        tdSql.checkData(39, 0, 35)
+        tdSql.checkData(40, 0, 40)   #
+        tdSql.checkData(41, 0, 40)
+        tdSql.checkData(44, 0, 40)
+        tdSql.checkData(45, 0, None) #
+        tdSql.checkData(46, 0, None)
+        tdSql.checkData(49, 0, None)
+        tdSql.checkData(50, 0, 50)   #
+        tdSql.checkData(51, 0, 50)
+        tdSql.checkData(54, 0, 50)
+        tdSql.checkData(55, 0, None) #
+        tdSql.checkData(56, 0, None)
+        tdSql.checkData(59, 0, None)
+        tdSql.checkData(60, 0, 55)   #
+
+        tdSql.checkData(0,  1, None) #
+        tdSql.checkData(1,  1, None)
+        tdSql.checkData(4,  1, None)
+        tdSql.checkData(5,  1, None) #
+        tdSql.checkData(6,  1, None)
+        tdSql.checkData(9,  1, None)
+        tdSql.checkData(10, 1, 10)   #
+        tdSql.checkData(11, 1, 10)
+        tdSql.checkData(14, 1, 10)
+        tdSql.checkData(15, 1, None) #
+        tdSql.checkData(16, 1, None)
+        tdSql.checkData(19, 1, None)
+        tdSql.checkData(20, 1, None) #
+        tdSql.checkData(21, 1, None)
+        tdSql.checkData(24, 1, None)
+        tdSql.checkData(25, 1, None) #
+        tdSql.checkData(26, 1, None)
+        tdSql.checkData(29, 1, None)
+        tdSql.checkData(30, 1, 30)   #
+        tdSql.checkData(31, 1, 30)
+        tdSql.checkData(34, 1, 30)
+        tdSql.checkData(35, 1, None) #
+        tdSql.checkData(36, 1, None)
+        tdSql.checkData(39, 1, None)
+        tdSql.checkData(40, 1, 40)   #
+        tdSql.checkData(41, 1, 40)
+        tdSql.checkData(44, 1, 40)
+        tdSql.checkData(45, 1, 45)   #
+        tdSql.checkData(46, 1, 45)
+        tdSql.checkData(49, 1, 45)
+        tdSql.checkData(50, 1, None) #
+        tdSql.checkData(51, 1, None)
+        tdSql.checkData(54, 1, None)
+        tdSql.checkData(55, 1, None) #
+        tdSql.checkData(56, 1, None)
+        tdSql.checkData(59, 1, None)
+        tdSql.checkData(60, 1, 60)   #
+
+        # test fill next
+        tdSql.query(f"select interp(c0),interp(c1) from {dbname}.{tbname1} range('2020-02-02 00:00:00', '2020-02-02 00:01:00') every(1s) fill(next)")
+        tdSql.checkRows(61)
+        tdSql.checkCols(2)
+        tdSql.checkData(0,  0, 0)    #
+        tdSql.checkData(1,  0, None)
+        tdSql.checkData(4,  0, None)
+        tdSql.checkData(5,  0, None) #
+        tdSql.checkData(6,  0, 10)
+        tdSql.checkData(9,  0, 10)
+        tdSql.checkData(10, 0, 10)   #
+        tdSql.checkData(11, 0, None)
+        tdSql.checkData(14, 0, None)
+        tdSql.checkData(15, 0, None) #
+        tdSql.checkData(16, 0, 20)
+        tdSql.checkData(19, 0, 20)
+        tdSql.checkData(20, 0, 20)   #
+        tdSql.checkData(21, 0, None)
+        tdSql.checkData(24, 0, None)
+        tdSql.checkData(25, 0, None) #
+        tdSql.checkData(26, 0, 30)
+        tdSql.checkData(29, 0, 30)
+        tdSql.checkData(30, 0, 30)   #
+        tdSql.checkData(31, 0, 35)
+        tdSql.checkData(34, 0, 35)
+        tdSql.checkData(35, 0, 35)   #
+        tdSql.checkData(36, 0, 40)
+        tdSql.checkData(39, 0, 40)
+        tdSql.checkData(40, 0, 40)   #
+        tdSql.checkData(41, 0, None)
+        tdSql.checkData(44, 0, None)
+        tdSql.checkData(45, 0, None) #
+        tdSql.checkData(46, 0, 50)
+        tdSql.checkData(49, 0, 50)
+        tdSql.checkData(50, 0, 50)   #
+        tdSql.checkData(51, 0, None)
+        tdSql.checkData(54, 0, None)
+        tdSql.checkData(55, 0, None) #
+        tdSql.checkData(56, 0, 55)
+        tdSql.checkData(59, 0, 55)
+        tdSql.checkData(60, 0, 55)   #
+
+        tdSql.checkData(0,  1, None) #
+        tdSql.checkData(1,  1, None)
+        tdSql.checkData(4,  1, None)
+        tdSql.checkData(5,  1, None) #
+        tdSql.checkData(6,  1, 10)
+        tdSql.checkData(9,  1, 10)
+        tdSql.checkData(10, 1, 10)   #
+        tdSql.checkData(11, 1, None)
+        tdSql.checkData(14, 1, None)
+        tdSql.checkData(15, 1, None) #
+        tdSql.checkData(16, 1, None)
+        tdSql.checkData(19, 1, None)
+        tdSql.checkData(20, 1, None) #
+        tdSql.checkData(21, 1, None)
+        tdSql.checkData(24, 1, None)
+        tdSql.checkData(25, 1, None) #
+        tdSql.checkData(26, 1, 30)
+        tdSql.checkData(29, 1, 30)
+        tdSql.checkData(30, 1, 30)   #
+        tdSql.checkData(31, 1, None)
+        tdSql.checkData(34, 1, None)
+        tdSql.checkData(35, 1, None) #
+        tdSql.checkData(36, 1, 40)
+        tdSql.checkData(39, 1, 40)
+        tdSql.checkData(40, 1, 40)   #
+        tdSql.checkData(41, 1, 45)
+        tdSql.checkData(44, 1, 45)
+        tdSql.checkData(45, 1, 45)   #
+        tdSql.checkData(46, 1, None)
+        tdSql.checkData(49, 1, None)
+        tdSql.checkData(50, 1, None) #
+        tdSql.checkData(51, 1, None)
+        tdSql.checkData(54, 1, None)
+        tdSql.checkData(55, 1, None) #
+        tdSql.checkData(56, 1, 60)
+        tdSql.checkData(59, 1, 60)
+        tdSql.checkData(60, 1, 60)   #
+
+        tdLog.printNoPrefix("==========step11:test multi-interp cases")
         tdSql.query(f"select interp(c0),interp(c1),interp(c2),interp(c3) from {dbname}.{tbname} range('2020-02-09 00:00:05', '2020-02-13 00:00:05') every(1d) fill(null)")
         tdSql.checkRows(5)
         tdSql.checkCols(4)
@@ -891,7 +1827,7 @@ class TDTestCase:
         for i in range (tdSql.queryCols):
             tdSql.checkData(0, i, 13)
 
-        tdLog.printNoPrefix("==========step11:test error cases")
+        tdLog.printNoPrefix("==========step12:test error cases")
 
         tdSql.error(f"select interp(c0) from {dbname}.{tbname}")
         tdSql.error(f"select interp(c0) from {dbname}.{tbname} range('2020-02-10 00:00:05', '2020-02-15 00:00:05')")
@@ -914,7 +1850,7 @@ class TDTestCase:
         tdSql.error(f"select interp('abcd') from {dbname}.{tbname} range('2020-02-10 00:00:05', '2020-02-15 00:00:05') every(1d) fill(null)")
         tdSql.error(f"select interp('中文字符') from {dbname}.{tbname} range('2020-02-10 00:00:05', '2020-02-15 00:00:05') every(1d) fill(null)")
 
-        tdLog.printNoPrefix("==========step12:stable cases")
+        tdLog.printNoPrefix("==========step13:stable cases")
 
         #tdSql.query(f"select interp(c0) from {dbname}.{stbname} range('2020-02-01 00:00:04', '2020-02-01 00:00:16') every(1s) fill(null)")
         #tdSql.checkRows(13)