diff --git a/src/tsdb/src/tsdbRead.c b/src/tsdb/src/tsdbRead.c
index cd421032cd963f1738ba7bcc480033ce50a3330c..b16337ed7a6537f341e53b7d47b4867ea0c011cd 100644
--- a/src/tsdb/src/tsdbRead.c
+++ b/src/tsdb/src/tsdbRead.c
@@ -1180,9 +1180,12 @@ static void copyOneRowFromMem(STsdbQueryHandle* pQueryHandle, int32_t capacity,
   char* pData = NULL;
 
   // the schema version info is embeded in SDataRow
-  int32_t numOfRowCols = schemaNCols(pSchema);
+  int32_t numOfRowCols = 0;
   if (pSchema == NULL) {
     pSchema = tsdbGetTableSchemaByVersion(pTable, dataRowVersion(row));
+    numOfRowCols = schemaNCols(pSchema);
+  } else {
+    numOfRowCols = schemaNCols(pSchema);
   }
   
   int32_t i = 0, j = 0;