diff --git a/src/query/inc/qAggMain.h b/src/query/inc/qAggMain.h
index 380e37645d083682ecbcd5865dce934878317d5d..a804d18b63ae6971cca74e687cf4393d60e19e23 100644
--- a/src/query/inc/qAggMain.h
+++ b/src/query/inc/qAggMain.h
@@ -71,14 +71,13 @@ extern "C" {
 #define TSDB_FUNC_BLKINFO      33
 
 #define TSDB_FUNC_CSUM         34
-
-#define TSDB_FUNC_HLL          35
-#define TSDB_FUNC_MODE         36
-#define TSDB_FUNC_SAMPLE       37
+#define TSDB_FUNC_MAVG         35
+#define TSDB_FUNC_SAMPLE       36
+#define TSDB_FUNC_MODE         37
 #define TSDB_FUNC_CEIL         38
 #define TSDB_FUNC_FLOOR        39
 #define TSDB_FUNC_ROUND        40
-#define TSDB_FUNC_MAVG         41
+#define TSDB_FUNC_HLL         41
 #define TSDB_FUNC_HISTOGRAM    42
 
 #define TSDB_FUNCSTATE_SO           0x1u    // single output
diff --git a/src/query/src/qAggMain.c b/src/query/src/qAggMain.c
index 926b65f64b52680f8039cec0387bb8aa3b0ce280..9a95e41336a74a4b07dec8765892bb9f377a5c9c 100644
--- a/src/query/src/qAggMain.c
+++ b/src/query/src/qAggMain.c
@@ -4413,7 +4413,7 @@ typedef struct {
   int32_t pos;
   double sum;
   int32_t numPoints;
-  int64_t* points;
+  double* points;
 } SMovingAvgInfo;
 
 static bool mavg_function_setup(SQLFunctionCtx *pCtx, SResultRowCellInfo* pResInfo) {
@@ -4422,10 +4422,10 @@ static bool mavg_function_setup(SQLFunctionCtx *pCtx, SResultRowCellInfo* pResIn
   }
 
   SMovingAvgInfo* mavgInfo = GET_ROWCELL_INTERBUF(pResInfo);
-  mavgInfo->pos = -1;
+  mavgInfo->pos = 0;
   mavgInfo->sum = 0;
   mavgInfo->numPoints = (int32_t)pCtx->param[0].i64;
-  mavgInfo->points = (int64_t*)((char*)mavgInfo + sizeof(mavgInfo));
+  mavgInfo->points = (double*)((char*)mavgInfo + sizeof(mavgInfo));
   return true;
 }
 
@@ -4445,96 +4445,169 @@ static void mavg_function(SQLFunctionCtx *pCtx) {
   switch (pCtx->inputType) {
     case TSDB_DATA_TYPE_INT: {
       int32_t *pData = (int32_t *)data;
-      int32_t *pOutput = (int32_t *)pCtx->pOutput;
+      double *pOutput = (double *)pCtx->pOutput;
       for (; i < pCtx->size && i >= 0; i += step) {
         if (pCtx->hasNull && isNull((const char*) &pData[i], pCtx->inputType)) {
           continue;
         }
 
-        pCumSumInfo->cumSum += pData[i];
-        *pTimestamp = (tsList != NULL) ? tsList[i] : 0;
-        SET_DOUBLE_VAL(pOutput, pCumSumInfo->cumSum);
+        if (mavgInfo->pos < mavgInfo->numPoints - 1) {
+          mavgInfo->points[mavgInfo->pos] = (double)pData[i];
+          mavgInfo->sum += pData[i];
+        } else {
+          int32_t pos = mavgInfo->pos % mavgInfo->numPoints;
+          if (mavgInfo->pos != mavgInfo->numPoints -1) {
+            mavgInfo->sum = mavgInfo->sum + (double)pData[i] - mavgInfo->points[pos];
+          } else {
+            mavgInfo->sum += (double)pData[i];
+          }
 
-        ++notNullElems;
-        pOutput += 1;
-        pTimestamp += 1;
+          mavgInfo->points[pos] = pData[i];
+
+          *pTimestamp = (tsList != NULL) ? tsList[i] : 0;
+          SET_DOUBLE_VAL(pOutput, mavgInfo->sum / mavgInfo->numPoints)
+          ++notNullElems;
+          pOutput += 1;
+          pTimestamp += 1;
+        }
+
+        ++mavgInfo->pos;
       }
       break;
     }
 
     case TSDB_DATA_TYPE_BIGINT: {
       int64_t *pData = (int64_t *)data;
-      int64_t *pOutput = (int64_t *)pCtx->pOutput;
+      double *pOutput = (double *)pCtx->pOutput;
       for (; i < pCtx->size && i >= 0; i += step) {
         if (pCtx->hasNull && isNull((const char*) &pData[i], pCtx->inputType)) {
           continue;
         }
 
-        pCumSumInfo->cumSum += pData[i];
-        *pTimestamp = (tsList != NULL) ? tsList[i] : 0;
-        SET_DOUBLE_VAL(pOutput, pCumSumInfo->cumSum);
+        if (mavgInfo->pos < mavgInfo->numPoints - 1) {
+          mavgInfo->points[mavgInfo->pos] = (double)pData[i];
+          mavgInfo->sum += pData[i];
+        } else {
+          int32_t pos = mavgInfo->pos % mavgInfo->numPoints;
+          if (mavgInfo->pos != mavgInfo->numPoints -1) {
+            mavgInfo->sum = mavgInfo->sum + (double)pData[i] - mavgInfo->points[pos];
+          } else {
+            mavgInfo->sum += (double)pData[i];
+          }
 
-        ++notNullElems;
-        pOutput += 1;
-        pTimestamp += 1;
+          mavgInfo->points[pos] = pData[i];
+
+          *pTimestamp = (tsList != NULL) ? tsList[i] : 0;
+          SET_DOUBLE_VAL(pOutput, mavgInfo->sum / mavgInfo->numPoints)
+          ++notNullElems;
+          pOutput += 1;
+          pTimestamp += 1;
+        }
+
+        ++mavgInfo->pos;
       }
       break;
     }
 
     case TSDB_DATA_TYPE_TINYINT: {
       int8_t *pData = (int8_t *)data;
-      int8_t *pOutput = (int8_t *)pCtx->pOutput;
+      double *pOutput = (double *)pCtx->pOutput;
       for (; i < pCtx->size && i >= 0; i += step) {
         if (pCtx->hasNull && isNull((const char*) &pData[i], pCtx->inputType)) {
           continue;
         }
 
-        pCumSumInfo->cumSum += pData[i];
-        *pTimestamp = (tsList != NULL) ? tsList[i] : 0;
-        SET_DOUBLE_VAL(pOutput, pCumSumInfo->cumSum);
+        if (mavgInfo->pos < mavgInfo->numPoints - 1) {
+          mavgInfo->points[mavgInfo->pos] = (double)pData[i];
+          mavgInfo->sum += pData[i];
+        } else {
+          int32_t pos = mavgInfo->pos % mavgInfo->numPoints;
+          if (mavgInfo->pos != mavgInfo->numPoints -1) {
+            mavgInfo->sum = mavgInfo->sum + (double)pData[i] - mavgInfo->points[pos];
+          } else {
+            mavgInfo->sum += (double)pData[i];
+          }
 
-        ++notNullElems;
-        pOutput += 1;
-        pTimestamp += 1;
+          mavgInfo->points[pos] = pData[i];
+
+          *pTimestamp = (tsList != NULL) ? tsList[i] : 0;
+          SET_DOUBLE_VAL(pOutput, mavgInfo->sum / mavgInfo->numPoints)
+          ++notNullElems;
+          pOutput += 1;
+          pTimestamp += 1;
+        }
+
+        ++mavgInfo->pos;
       }
+
       break;
     }
 
     case TSDB_DATA_TYPE_SMALLINT: {
       int16_t *pData = (int16_t *)data;
-      int16_t *pOutput = (int16_t *)pCtx->pOutput;
+      double *pOutput = (double *)pCtx->pOutput;
       for (; i < pCtx->size && i >= 0; i += step) {
         if (pCtx->hasNull && isNull((const char*) &pData[i], pCtx->inputType)) {
           continue;
         }
 
-        pCumSumInfo->cumSum += pData[i];
-        *pTimestamp = (tsList != NULL) ? tsList[i] : 0;
-        SET_DOUBLE_VAL(pOutput, pCumSumInfo->cumSum);
+        if (mavgInfo->pos < mavgInfo->numPoints - 1) {
+          mavgInfo->points[mavgInfo->pos] = (double)pData[i];
+          mavgInfo->sum += pData[i];
+        } else {
+          int32_t pos = mavgInfo->pos % mavgInfo->numPoints;
+          if (mavgInfo->pos != mavgInfo->numPoints -1) {
+            mavgInfo->sum = mavgInfo->sum + (double)pData[i] - mavgInfo->points[pos];
+          } else {
+            mavgInfo->sum += (double)pData[i];
+          }
 
-        ++notNullElems;
-        pOutput += 1;
-        pTimestamp += 1;
+          mavgInfo->points[pos] = pData[i];
+
+          *pTimestamp = (tsList != NULL) ? tsList[i] : 0;
+          SET_DOUBLE_VAL(pOutput, mavgInfo->sum / mavgInfo->numPoints)
+          ++notNullElems;
+          pOutput += 1;
+          pTimestamp += 1;
+        }
+
+        ++mavgInfo->pos;
       }
+
       break;
     }
 
     case TSDB_DATA_TYPE_FLOAT: {
       float *pData = (float *)data;
-      float *pOutput = (float *)pCtx->pOutput;
+      double *pOutput = (double *)pCtx->pOutput;
       for (; i < pCtx->size && i >= 0; i += step) {
         if (pCtx->hasNull && isNull((const char*) &pData[i], pCtx->inputType)) {
           continue;
         }
 
-        pCumSumInfo->cumSum += pData[i];
-        *pTimestamp = (tsList != NULL) ? tsList[i] : 0;
-        SET_DOUBLE_VAL(pOutput, pCumSumInfo->cumSum);
+        if (mavgInfo->pos < mavgInfo->numPoints - 1) {
+          mavgInfo->points[mavgInfo->pos] = (double)pData[i];
+          mavgInfo->sum += pData[i];
+        } else {
+          int32_t pos = mavgInfo->pos % mavgInfo->numPoints;
+          if (mavgInfo->pos != mavgInfo->numPoints -1) {
+            mavgInfo->sum = mavgInfo->sum + (double)pData[i] - mavgInfo->points[pos];
+          } else {
+            mavgInfo->sum += (double)pData[i];
+          }
 
-        ++notNullElems;
-        pOutput += 1;
-        pTimestamp += 1;
+          mavgInfo->points[pos] = pData[i];
+
+          *pTimestamp = (tsList != NULL) ? tsList[i] : 0;
+          SET_DOUBLE_VAL(pOutput, mavgInfo->sum / mavgInfo->numPoints)
+          ++notNullElems;
+          pOutput += 1;
+          pTimestamp += 1;
+        }
+
+        ++mavgInfo->pos;
       }
+
       break;
     }
 
@@ -4546,16 +4619,31 @@ static void mavg_function(SQLFunctionCtx *pCtx) {
           continue;
         }
 
-        pCumSumInfo->cumSum += pData[i];
-        *pTimestamp = (tsList != NULL) ? tsList[i] : 0;
-        SET_DOUBLE_VAL(pOutput, pCumSumInfo->cumSum);
+        if (mavgInfo->pos < mavgInfo->numPoints - 1) {
+          mavgInfo->points[mavgInfo->pos] = (double)pData[i];
+          mavgInfo->sum += pData[i];
+        } else {
+          int32_t pos = mavgInfo->pos % mavgInfo->numPoints;
+          if (mavgInfo->pos != mavgInfo->numPoints - 1) {
+            mavgInfo->sum = mavgInfo->sum + (double)pData[i] - mavgInfo->points[pos];
+          } else {
+            mavgInfo->sum += (double)pData[i];
+          }
 
-        ++notNullElems;
-        pOutput += 1;
-        pTimestamp += 1;
+          mavgInfo->points[pos] = pData[i];
+
+          *pTimestamp = (tsList != NULL) ? tsList[i] : 0;
+          SET_DOUBLE_VAL(pOutput, mavgInfo->sum / mavgInfo->numPoints)
+          ++notNullElems;
+          pOutput += 1;
+          pTimestamp += 1;
+        }
+
+        ++mavgInfo->pos;
       }
       break;
     }
+
     default:
       qError("error input type");
   }
@@ -4568,7 +4656,179 @@ static void mavg_function(SQLFunctionCtx *pCtx) {
   }
 }
 
+//////////////////////////////////////////////////////////////////////////////////
+typedef struct  {
+  int32_t notNullElems;
+  int32_t      num;
+  tValuePair **res;
+} SSampleFuncInfo;
+
+static void sampleValuePairAssign(tValuePair *dst, tVariant* srcVariant, int64_t tsKey, char *pTags, SExtTagsInfo *pTagInfo) {
+  dst->timestamp = tsKey;
+  tVariantAssign(&dst->v, srcVariant);
+
+  int32_t size = 0;
+
+  for (int32_t i = 0; i < pTagInfo->numOfTagCols; ++i) {
+    SQLFunctionCtx* ctx = pTagInfo->pTagCtxList[i];
+    if (ctx->functionId == TSDB_FUNC_TS_DUMMY) {
+      ctx->tag.nType = TSDB_DATA_TYPE_BIGINT;
+      ctx->tag.i64 = tsKey;
+    }
+
+    tVariantDump(&ctx->tag, dst->pTags + size, ctx->tag.nType, true);
+    size += pTagInfo->pTagCtxList[i]->outputBytes;
+  }
+
+}
+
+
+static void do_sample_function_add(SSampleFuncInfo *pInfo, int32_t maxLen, void *pData, int64_t ts, uint16_t type, SExtTagsInfo *pTagInfo, char *pTags) {
+  tVariant val = {0};
+  tVariantCreateFromBinary(&val, pData, tDataTypes[type].bytes, type);
+
+  tValuePair **pList = pInfo->res;
+  assert(pList != NULL);
+
+  pInfo->notNullElems++;
+  if (pInfo->num < maxLen) {
+    sampleValuePairAssign(pList[pInfo->num], &val, ts, pTags, pTagInfo);
+    pInfo->num++;
+  } else {
+    int32_t j = rand() % (pInfo->notNullElems);
+    if (j < maxLen) {
+      sampleValuePairAssign(pList[j], &val, ts, pTags, pTagInfo);
+    }
+  }
+}
+
+
+static void copySampleFuncRes(SQLFunctionCtx *pCtx, int32_t type) {
+  SResultRowCellInfo *pResInfo = GET_RES_INFO(pCtx);
+  SSampleFuncInfo *pRes = GET_ROWCELL_INTERBUF(pResInfo);
+
+  tValuePair **tvp = pRes->res;
+
+  int32_t step = QUERY_ASC_FORWARD_STEP;
+  int32_t len = (int32_t)(GET_RES_INFO(pCtx)->numOfRes);
+
+  for (int32_t i = 0; i < len; ++i) {
+    char* output = pCtx->pOutput;
+    tVariantDump(&tvp[i]->v, (char*)output, type, true);
+    output += step * (pCtx->outputBytes);
+  }
+
+  // set the output timestamp of each record.
+  TSKEY *output = pCtx->ptsOutputBuf;
+  for (int32_t i = 0; i < len; ++i, output += step) {
+    *output = tvp[i]->timestamp;
+  }
 
+  // set the corresponding tag data for each record
+  // todo check malloc failure
+  char **pData = calloc(pCtx->tagInfo.numOfTagCols, POINTER_BYTES);
+  for (int32_t i = 0; i < pCtx->tagInfo.numOfTagCols; ++i) {
+    pData[i] = pCtx->tagInfo.pTagCtxList[i]->pOutput;
+  }
+
+  for (int32_t i = 0; i < len; ++i, output += step) {
+    int16_t offset = 0;
+    for (int32_t j = 0; j < pCtx->tagInfo.numOfTagCols; ++j) {
+      memcpy(pData[j], tvp[i]->pTags + offset, (size_t)pCtx->tagInfo.pTagCtxList[j]->outputBytes);
+      offset += pCtx->tagInfo.pTagCtxList[j]->outputBytes;
+      pData[j] += pCtx->tagInfo.pTagCtxList[j]->outputBytes;
+    }
+  }
+
+  tfree(pData);
+}
+
+/*
+ * +-----------------------------------+-------------one value pair-----------+------------next value pair-----------+
+ * |-------------pointer area----------|----ts---+-----+-----n tags-----------|----ts---+-----+-----n tags-----------|
+ * +..[Value Pointer1][Value Pointer2].|timestamp|value|tags1|tags2|....|tagsn|timestamp|value|tags1|tags2|....|tagsn+
+ */
+static void buildSampleFuncStruct(SSampleFuncInfo *pSampleFuncInfo, SQLFunctionCtx *pCtx) {
+  char *tmp = (char *)pSampleFuncInfo + sizeof(SSampleFuncInfo);
+  pSampleFuncInfo->res = (tValuePair**) tmp;
+  tmp += POINTER_BYTES * pCtx->param[0].i64;
+
+  size_t size = sizeof(tValuePair) + pCtx->tagInfo.tagsLen;
+
+  for (int32_t i = 0; i < pCtx->param[0].i64; ++i) {
+    pSampleFuncInfo->res[i] = (tValuePair*) tmp;
+    pSampleFuncInfo->res[i]->pTags = tmp + sizeof(tValuePair);
+    tmp += size;
+  }
+}
+
+
+static bool sample_function_setup(SQLFunctionCtx *pCtx, SResultRowCellInfo* pResInfo) {
+  if (!function_setup(pCtx, pResInfo)) {
+    return false;
+  }
+
+  SSampleFuncInfo *pRes = GET_ROWCELL_INTERBUF(pResInfo);
+  buildSampleFuncStruct(pRes, pCtx);
+  srand(taosSafeRand());
+  pRes->notNullElems = 0;
+  return true;
+}
+
+static void sample_function(SQLFunctionCtx *pCtx) {
+  int32_t notNullElems = 0;
+
+  SResultRowCellInfo *pResInfo = GET_RES_INFO(pCtx);
+  SSampleFuncInfo *pRes = GET_ROWCELL_INTERBUF(pResInfo);
+
+  assert(pRes->num >= 0);
+
+  if ((void *)pRes->res[0] != (void *)((char *)pRes + sizeof(SSampleFuncInfo) + POINTER_BYTES * pCtx->param[0].i64)) {
+    buildSampleFuncStruct(pRes, pCtx);
+  }
+
+  for (int32_t i = 0; i < pCtx->size; ++i) {
+    char *data = GET_INPUT_DATA(pCtx, i);
+    if (pCtx->hasNull && isNull(data, pCtx->inputType)) {
+      continue;
+    }
+
+    notNullElems++;
+
+    // NOTE: Set the default timestamp if it is missing [todo refactor]
+    TSKEY ts = (pCtx->ptsList != NULL)? GET_TS_DATA(pCtx, i):0;
+    do_sample_function_add(pRes, (int32_t)pCtx->param[0].i64, data, ts, pCtx->inputType, &pCtx->tagInfo, NULL);
+  }
+
+  if (!pCtx->hasNull) {
+    assert(pCtx->size == notNullElems);
+  }
+
+  // treat the result as only one result
+  SET_VAL(pCtx, notNullElems, 1);
+
+  if (notNullElems > 0) {
+    pResInfo->hasResult = DATA_SET_FLAG;
+  }
+}
+
+
+static void sample_func_finalizer(SQLFunctionCtx *pCtx) {
+  SResultRowCellInfo *pResInfo = GET_RES_INFO(pCtx);
+  SSampleFuncInfo *pRes = GET_ROWCELL_INTERBUF(pResInfo);
+
+  if (pRes->num == 0) {  // no result
+    assert(pResInfo->hasResult != DATA_SET_FLAG);
+  }
+
+
+  GET_TRUE_DATA_TYPE();
+  copySampleFuncRes(pCtx, type);
+
+  doFinalizer(pCtx);
+}
+
+//////////////////////////////////////////////////////////////////////////////////
 
 /////////////////////////////////////////////////////////////////////////////////////////////
 /*
@@ -5015,4 +5275,28 @@ SAggFunctionInfo aAggs[] = {{
         noop1,
         dataBlockRequired,
     },
+    {
+        // 35
+        "mavg",
+        TSDB_FUNC_MAVG,
+        TSDB_FUNC_INVALID_ID,
+        TSDB_FUNCSTATE_MO | TSDB_FUNCSTATE_STABLE | TSDB_FUNCSTATE_NEED_TS | TSDB_FUNCSTATE_SELECTIVITY,
+        mavg_function_setup,
+        mavg_function,
+        doFinalizer,
+        noop1,
+        dataBlockRequired,
+    },
+    {
+        // 36
+        "sample",
+        TSDB_FUNC_SAMPLE,
+        TSDB_FUNC_INVALID_ID,
+        TSDB_FUNCSTATE_MO | TSDB_FUNCSTATE_NEED_TS | TSDB_FUNCSTATE_SELECTIVITY,
+        sample_function_setup,
+        sample_function,
+        sample_func_finalizer,
+        noop1,
+        dataBlockRequired,
+    },
 };