Resolve the inconsistency problem of distinct count in offline mode

**Bug Description**

Now we may get the inconsistent result for SQL with groupby.

The issue mentions inconsistent results for SQL with GROUP BY in offline mode. Look for code handling distinct count aggregation in the offline execution engine. Start by searching for 'distinct count' or 'GROUP BY' in the codebase, particularly in query execution or aggregation modules. Examine test files related to offline SQL execution to understand the expected behavior and identify where the inconsistency occurs.

索引モデルが issue の本文から書いたものです。