From 6f2ac5ba7221a3c90e2e7e02ab762b7bf7e28e6f Mon Sep 17 00:00:00 2001
From: Haojun Liao <hjliao@taosdata.com>
Date: Tue, 12 Jul 2022 21:07:12 +0800
Subject: [PATCH] fix(query): always generated  results for last_row query if
 rows exists.

---
 source/dnode/vnode/src/tsdb/tsdbCacheRead.c |  3 ++-
 source/libs/function/src/builtins.c         |  2 +-
 source/libs/function/src/builtinsimpl.c     | 28 +++++++++++++--------
 3 files changed, 20 insertions(+), 13 deletions(-)

diff --git a/source/dnode/vnode/src/tsdb/tsdbCacheRead.c b/source/dnode/vnode/src/tsdb/tsdbCacheRead.c
index 750797cd69..5c09c7663f 100644
--- a/source/dnode/vnode/src/tsdb/tsdbCacheRead.c
+++ b/source/dnode/vnode/src/tsdb/tsdbCacheRead.c
@@ -30,6 +30,7 @@ typedef struct SLastrowReader {
 } SLastrowReader;
 
 static void saveOneRow(STSRow* pRow, SSDataBlock* pBlock, SLastrowReader* pReader, const int32_t* slotIds) {
+  ASSERT(pReader->numOfCols <= taosArrayGetSize(pBlock->pDataBlock));
   int32_t numOfRows = pBlock->info.rows;
 
   SColVal colVal = {0};
@@ -69,7 +70,6 @@ int32_t tsdbLastRowReaderOpen(void* pVnode, int32_t type, SArray* pTableIdList,
   p->type = type;
   p->pVnode = pVnode;
   p->numOfCols = numOfCols;
-  p->transferBuf = taosMemoryCalloc(p->numOfCols, POINTER_BYTES);
 
   if (taosArrayGetSize(pTableIdList) == 0) {
     *pReader = p;
@@ -80,6 +80,7 @@ int32_t tsdbLastRowReaderOpen(void* pVnode, int32_t type, SArray* pTableIdList,
   p->pSchema = metaGetTbTSchema(p->pVnode->pMeta, pKeyInfo->uid, -1);
   p->pTableList = pTableIdList;
 
+  p->transferBuf = taosMemoryCalloc(p->pSchema->numOfCols, POINTER_BYTES);
   for (int32_t i = 0; i < p->pSchema->numOfCols; ++i) {
     if (IS_VAR_DATA_TYPE(p->pSchema->columns[i].type)) {
       p->transferBuf[i] = taosMemoryMalloc(p->pSchema->columns[i].bytes);
diff --git a/source/libs/function/src/builtins.c b/source/libs/function/src/builtins.c
index b4e0e82ac6..1b8b39a76e 100644
--- a/source/libs/function/src/builtins.c
+++ b/source/libs/function/src/builtins.c
@@ -2217,7 +2217,7 @@ const SBuiltinFuncDefinition funcMgtBuiltins[] = {
   {
     .name = "last_row",
     .type = FUNCTION_TYPE_LAST_ROW,
-    .classification = FUNC_MGT_AGG_FUNC | FUNC_MGT_MULTI_RES_FUNC | FUNC_MGT_SELECT_FUNC | FUNC_MGT_TIMELINE_FUNC,
+    .classification = FUNC_MGT_AGG_FUNC | FUNC_MGT_MULTI_RES_FUNC | FUNC_MGT_SELECT_FUNC | FUNC_MGT_TIMELINE_FUNC | FUNC_MGT_IMPLICIT_TS_FUNC,
     .translateFunc = translateFirstLast,
     .getEnvFunc   = getFirstLastFuncEnv,
     .initFunc     = functionSetup,
diff --git a/source/libs/function/src/builtinsimpl.c b/source/libs/function/src/builtinsimpl.c
index 5dee2e8480..0324a6bae0 100644
--- a/source/libs/function/src/builtinsimpl.c
+++ b/source/libs/function/src/builtinsimpl.c
@@ -80,8 +80,10 @@ typedef struct STopBotRes {
 } STopBotRes;
 
 typedef struct SFirstLastRes {
-  bool    hasResult;
-  bool    isNull;  // used for last_row function only
+  bool hasResult;
+  // used for last_row function only, isNullRes in SResultRowEntry can not be passed to downstream.So,
+  // this attribute is required
+  bool isNull;
   int32_t bytes;
   char    buf[];
 } SFirstLastRes;
@@ -2900,7 +2902,7 @@ int32_t firstLastFinalize(SqlFunctionCtx* pCtx, SSDataBlock* pBlock) {
   pResInfo->isNullRes = (pResInfo->numOfRes == 0) ? 1 : 0;
 
   SFirstLastRes* pRes = GET_ROWCELL_INTERBUF(pResInfo);
-  colDataAppend(pCol, pBlock->info.rows, pRes->buf, pResInfo->isNullRes);
+  colDataAppend(pCol, pBlock->info.rows, pRes->buf, pRes->isNull||pResInfo->isNullRes);
   // handle selectivity
   STuplePos* pTuplePos = (STuplePos*)(pRes->buf + pRes->bytes + sizeof(TSKEY));
   setSelectivityValue(pCtx, pBlock, pTuplePos, pBlock->info.rows);
@@ -5956,24 +5958,28 @@ int32_t lastrowFunction(SqlFunctionCtx* pCtx) {
 
   int32_t type = pInputCol->info.type;
   int32_t bytes = pInputCol->info.bytes;
+
   pInfo->bytes = bytes;
 
+  // last_row function does not ignore the null value
   for (int32_t i = pInput->numOfRows + pInput->startRowIndex - 1; i >= pInput->startRowIndex; --i) {
-    if (pInputCol->hasNull && colDataIsNull_s(pInputCol, i)) {
-      continue;
-    }
-
     numOfElems++;
 
     char* data = colDataGetData(pInputCol, i);
     TSKEY cts = getRowPTs(pInput->pPTS, i);
     if (pResInfo->numOfRes == 0 || *(TSKEY*)(pInfo->buf + bytes) < cts) {
-      if (IS_VAR_DATA_TYPE(type)) {
-        bytes = varDataTLen(data);
-        pInfo->bytes = bytes;
+
+      if (colDataIsNull_s(pInputCol, i)) {
+        pInfo->isNull = true;
+      } else {
+        if (IS_VAR_DATA_TYPE(type)) {
+          bytes = varDataTLen(data);
+          pInfo->bytes = bytes;
+        }
+
+        memcpy(pInfo->buf, data, bytes);
       }
 
-      memcpy(pInfo->buf, data, bytes);
       *(TSKEY*)(pInfo->buf + bytes) = cts;
 
       pInfo->hasResult = true;
-- 
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