diff --git a/source/dnode/vnode/src/tsdb/tsdbCacheRead.c b/source/dnode/vnode/src/tsdb/tsdbCacheRead.c
index fd5e8eb6e0..cf2e348fb2 100644
--- a/source/dnode/vnode/src/tsdb/tsdbCacheRead.c
+++ b/source/dnode/vnode/src/tsdb/tsdbCacheRead.c
@@ -41,6 +41,13 @@ static int32_t saveOneRow(SArray* pRow, SSDataBlock* pBlock, SCacheRowsReader* p
         int32_t   slotId = slotIds[i];
         SLastCol* pColVal = (SLastCol*)taosArrayGet(pRow, slotId);
 
+        // add check for null value, caused by the modification of table schema (new column added).
+        if (pColVal == NULL) {
+          p->ts = 0;
+          p->isNull = true;
+          continue;
+        }
+
         p->ts = pColVal->ts;
         p->isNull = !COL_VAL_IS_VALUE(&pColVal->colVal);
         allNullRow = p->isNull & allNullRow;
diff --git a/source/dnode/vnode/src/tsdb/tsdbRead.c b/source/dnode/vnode/src/tsdb/tsdbRead.c
index e9bb7e3d09..eb083a75cd 100644
--- a/source/dnode/vnode/src/tsdb/tsdbRead.c
+++ b/source/dnode/vnode/src/tsdb/tsdbRead.c
@@ -3942,6 +3942,7 @@ int32_t tsdbReaderOpen(SVnode* pVnode, SQueryTableDataCond* pCond, void* pTableL
 _err:
   tsdbError("failed to create data reader, code:%s %s", tstrerror(code), idstr);
   tsdbReaderClose(pReader);
+  *ppReader = NULL;   // reset the pointer value.
   return code;
 }