Merge pull request #19101 from taosdata/feature/3_liaohj

fix(query): set start row index for desc scan.

source/dnode/vnode/src/tsdb/tsdbMergeTree.c

@@ -158,9 +158,9 @@ static SBlockData *loadLastBlock(SLDataIter *pIter, const char *idStr) {
             pBlock, el, idStr);
 
   pInfo->blockIndex[pInfo->currentLoadBlockIndex] = pIter->iSttBlk;
-  tsdbDebug("last block index list:%d, %d, %s", pInfo->blockIndex[0], pInfo->blockIndex[1], idStr);
-
   pIter->iRow = (pIter->backward) ? pInfo->blockData[pInfo->currentLoadBlockIndex].nRow : -1;
+
+  tsdbDebug("last block index list:%d, %d, rowIndex:%d %s", pInfo->blockIndex[0], pInfo->blockIndex[1], pIter->iRow, idStr);
   return &pInfo->blockData[pInfo->currentLoadBlockIndex];
 
 _exit:
@@ -419,6 +419,7 @@ static void findNextValidRow(SLDataIter *pIter, const char *idStr) {
       pBlockData->aUid != NULL) {
     i = binarySearchForStartRowIndex((uint64_t *)pBlockData->aUid, pBlockData->nRow, pIter->uid, pIter->backward);
     if (i == -1) {
+      tsdbDebug("failed to find the data in pBlockData, uid:%"PRIu64" , %s", pIter->uid, idStr);
       pIter->iRow = -1;
       return;
     }
@@ -500,7 +501,12 @@ bool tLDataIterNextRow(SLDataIter *pIter, const char *idStr) {
 
     if (iBlockL != pIter->iSttBlk) {
       pBlockData = loadLastBlock(pIter, idStr);
-      pIter->iRow += step;
+      if (pBlockData == NULL) {
+        goto _exit;
+      }
+
+      // set start row index
+      pIter->iRow = pIter->backward? pBlockData->nRow-1:0;
     }
   }