diff --git a/be/src/olap/memtable.cpp b/be/src/olap/memtable.cpp
index 16aa81ee61..6bc82b052c 100644
--- a/be/src/olap/memtable.cpp
+++ b/be/src/olap/memtable.cpp
@@ -238,11 +238,6 @@ void MemTable::_aggregate_two_row_in_block(vectorized::MutableBlock& mutable_blo
 }
 void MemTable::_put_into_output(vectorized::Block& in_block) {
     SCOPED_RAW_TIMER(&_stat.put_into_output_ns);
-    if (_keys_type == KeysType::DUP_KEYS && _schema->num_key_columns() == 0) {
-        // skip sort if the table is dup table without keys
-        _output_mutable_block.swap(_input_mutable_block);
-        return;
-    }
     std::vector<int> row_pos_vec;
     DCHECK(in_block.rows() <= std::numeric_limits<int>::max());
     row_pos_vec.reserve(in_block.rows());
@@ -470,8 +465,12 @@ Status MemTable::_do_flush() {
     SCOPED_CONSUME_MEM_TRACKER(_flush_mem_tracker);
     int same_keys_num = _sort();
     if (_keys_type == KeysType::DUP_KEYS || same_keys_num == 0) {
-        vectorized::Block in_block = _input_mutable_block.to_block();
-        _put_into_output(in_block);
+        if (_keys_type == KeysType::DUP_KEYS && _schema->num_key_columns() == 0) {
+            _output_mutable_block.swap(_input_mutable_block);
+        } else {
+            vectorized::Block in_block = _input_mutable_block.to_block();
+            _put_into_output(in_block);
+        }
     } else {
         _aggregate<true>();
     }