Thank for your reply!
I didn't get an error message but result always is null object. However, I sure there are records in table that i want query.
When I debug in my code, I got
CMSContext.CurrentUser is object have full name is "Public Anonymous User" and it isn't null.
I tried uses
ConnectionHelper.ExecuteQuery(querySql, new QueryDataParameters(), QueryTypeEnum.SQLQuery,false);
but it do not work correctly.
Do you have other way to retrieve data?