diff --git a/src/sql/engine/basic/ob_temp_column_store.cpp b/src/sql/engine/basic/ob_temp_column_store.cpp
index fbb9f5adaa..687349a07a 100644
--- a/src/sql/engine/basic/ob_temp_column_store.cpp
+++ b/src/sql/engine/basic/ob_temp_column_store.cpp
@@ -171,6 +171,7 @@ int ObTempColumnStore::Iterator::get_next_batch(const ObExprPtrIArray &exprs,
                                                 int64_t &read_rows)
 {
   int ret = OB_SUCCESS;
+  read_rows = 0;
   if (OB_UNLIKELY(exprs.count() != column_store_->get_col_cnt())) {
     ret = OB_INVALID_ARGUMENT;
     LOG_WARN("column count mismatch", K(ret), K(exprs.count()), K(column_store_->get_col_cnt()));
diff --git a/src/sql/engine/basic/ob_temp_column_store.h b/src/sql/engine/basic/ob_temp_column_store.h
index f518a684d7..9357e344fc 100644
--- a/src/sql/engine/basic/ob_temp_column_store.h
+++ b/src/sql/engine/basic/ob_temp_column_store.h
@@ -288,15 +288,18 @@ template<>
 inline int ObTempColumnStore::from_vector(ObBitmapNullVectorBase *vec, ObExpr *expr, ObEvalCtx &ctx,
                                           const int64_t start_pos, const int64_t size)
 {
-  const uint16_t flag = vec->get_flag();
-  ObBitVector &nulls = expr->get_nulls(ctx);
-  nulls.reset(size);
-  for (int64_t idx = start_pos; idx < size; ++idx) {
-    if (vec->is_null(idx)) {
-      nulls.set(idx - start_pos);
+  // reuse null vector memory if there is no null data
+  if (vec->has_null()) {
+    const uint16_t flag = vec->get_flag();
+    ObBitVector &nulls = expr->get_nulls(ctx);
+    nulls.reset(size - start_pos);
+    for (int64_t idx = start_pos; idx < size; ++idx) {
+      if (vec->is_null(idx)) {
+        nulls.set(idx - start_pos);
+      }
     }
+    vec->from(&nulls, flag);
   }
-  vec->from(&nulls, flag);
   return common::OB_SUCCESS;
 }
 
diff --git a/src/sql/engine/basic/ob_temp_row_store.cpp b/src/sql/engine/basic/ob_temp_row_store.cpp
index d16b228670..0a95af1e23 100644
--- a/src/sql/engine/basic/ob_temp_row_store.cpp
+++ b/src/sql/engine/basic/ob_temp_row_store.cpp
@@ -263,6 +263,7 @@ int ObTempRowStore::Iterator::get_next_batch(const ObExprPtrIArray &exprs,
                                              const ObCompactRow **stored_rows)
 {
   int ret = OB_SUCCESS;
+  read_rows = 0;
   if (OB_FAIL(row_store_->init_batch_ctx())) {
     LOG_WARN("init batch ctx failed", K(ret));
   } else if (OB_UNLIKELY(NULL == cur_blk_ || !cur_blk_->contain(cur_blk_id_))) {
@@ -340,6 +341,7 @@ int ObTempRowStore::Iterator::get_next_batch(const int64_t max_rows,
                                              int64_t &read_rows,
                                              const ObCompactRow **stored_rows) {
   int ret = OB_SUCCESS;
+  read_rows = 0;
   if (OB_ISNULL(stored_rows)) {
     ret = OB_INVALID_ARGUMENT;
     LOG_WARN("stored rows is null", K(ret));