From ede4a57c99de44d33e64ef5baddb9dc88ce835c7 Mon Sep 17 00:00:00 2001
From: Ganlin Zhao <ganlinzhao@hotmail.com>
Date: Mon, 16 May 2022 19:36:04 +0800
Subject: [PATCH] enh(query): tail function handle offset param

---
 source/libs/function/src/builtins.c     | 11 +++++++----
 source/libs/function/src/builtinsimpl.c | 14 +++++++++++---
 2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/source/libs/function/src/builtins.c b/source/libs/function/src/builtins.c
index 51f30aca21..e41e3c7c39 100644
--- a/source/libs/function/src/builtins.c
+++ b/source/libs/function/src/builtins.c
@@ -387,7 +387,8 @@ static int32_t translateSample(SFunctionNode* pFunc, char* pErrBuf, int32_t len)
 }
 
 static int32_t translateTail(SFunctionNode* pFunc, char* pErrBuf, int32_t len) {
-  if (2 != LIST_LENGTH(pFunc->pParameterList)) {
+  int32_t numOfParams = LIST_LENGTH(pFunc->pParameterList);
+  if (2 != numOfParams && 3 != numOfParams) {
     return invaildFuncParaNumErrMsg(pErrBuf, len, pFunc->functionName);
   }
 
@@ -397,9 +398,11 @@ static int32_t translateTail(SFunctionNode* pFunc, char* pErrBuf, int32_t len) {
                            "The input parameter of TAIL function can only be column");
   }
 
-  uint8_t paraType = ((SExprNode*)nodesListGetNode(pFunc->pParameterList, 1))->resType.type;
-  if (!IS_INTEGER_TYPE(paraType)) {
-    return invaildFuncParaTypeErrMsg(pErrBuf, len, pFunc->functionName);
+  for (int32_t i = 1; i < numOfParams; ++i) {
+    uint8_t paraType = ((SExprNode*)nodesListGetNode(pFunc->pParameterList, i))->resType.type;
+    if (!IS_INTEGER_TYPE(paraType)) {
+      return invaildFuncParaTypeErrMsg(pErrBuf, len, pFunc->functionName);
+    }
   }
 
   SExprNode* pCol = (SExprNode*)nodesListGetNode(pFunc->pParameterList, 0);
diff --git a/source/libs/function/src/builtinsimpl.c b/source/libs/function/src/builtinsimpl.c
index add33adb08..479a11ca4a 100644
--- a/source/libs/function/src/builtinsimpl.c
+++ b/source/libs/function/src/builtinsimpl.c
@@ -3177,7 +3177,11 @@ bool tailFunctionSetup(SqlFunctionCtx *pCtx, SResultRowEntryInfo *pResultInfo) {
   STailInfo *pInfo = GET_ROWCELL_INTERBUF(pResultInfo);
   pInfo->numAdded = 0;
   pInfo->numOfPoints = pCtx->param[1].param.i;
-  pInfo->offset = pCtx->param[2].param.i;
+  if (pCtx->numOfParams == 4) {
+    pInfo->offset = pCtx->param[2].param.i;
+  } else {
+    pInfo->offset = 0;
+  }
   pInfo->colType = pCtx->resDataInfo.type;
   pInfo->colBytes = pCtx->resDataInfo.bytes;
   if ((pInfo->numOfPoints < 1 || pInfo->numOfPoints > TAIL_MAX_POINTS_NUM) ||
@@ -3236,8 +3240,12 @@ int32_t tailFunction(SqlFunctionCtx* pCtx) {
   SColumnInfoData* pOutput = (SColumnInfoData*)pCtx->pOutput;
 
   int32_t startOffset = pCtx->offset;
-  pInfo->numOfPoints = MIN(pInfo->numOfPoints, pInput->numOfRows);
-  for (int32_t i = pInput->startRowIndex; i < pInput->numOfRows + pInput->startRowIndex; i += 1) {
+  if (pInfo->offset >= pInput->numOfRows) {
+    return 0;
+  } else {
+    pInfo->numOfPoints = MIN(pInfo->numOfPoints, pInput->numOfRows - pInfo->offset);
+  }
+  for (int32_t i = pInput->startRowIndex; i < pInput->numOfRows + pInput->startRowIndex - pInfo->offset; i += 1) {
 
     char* data = colDataGetData(pInputCol, i);
     doTailAdd(pInfo, data, tsList[i], colDataIsNull_s(pInputCol, i));
-- 
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