[TD-1568]fix tdMergeDataCols compare key bug

src/common/inc/tdataformat.h

@@ -289,6 +289,11 @@ static FORCE_INLINE TKEY dataColsTKeyFirst(SDataCols *pCols) {
   }
 }
 
+static FORCE_INLINE TSKEY dataColsKeyAtRow(SDataCols *pCols, int row) {
+  ASSERT(row < pCols->numOfRows);
+  return dataColsKeyAt(pCols, row);
+}
+
 static FORCE_INLINE TSKEY dataColsKeyFirst(SDataCols *pCols) {
   if (pCols->numOfRows) {
     return dataColsKeyAt(pCols, 0);

src/common/src/tdataformat.c

@@ -452,7 +452,7 @@ int tdMergeDataCols(SDataCols *target, SDataCols *source, int rowsToMerge, int *
 
   SDataCols *pTarget = NULL;
 
-  if ((target->numOfRows == 0) || (dataColsKeyLast(target) < dataColsKeyFirst(source))) {  // No overlap
+  if ((target->numOfRows == 0) || (dataColsKeyLast(target) < dataColsKeyAtRow(source, *pOffset))) {  // No overlap
     ASSERT(target->numOfRows + rowsToMerge <= target->maxPoints);
     for (int i = 0; i < rowsToMerge; i++) {
       for (int j = 0; j < source->numOfCols; j++) {