QSqlQuery执行带有参数的查询

Question

当我使用带参数的字符串时，我很难从QSqlQuery获取结果。以下工作正常：

str_filter = "SELECT region_pref FROM ut_users WHERE (user_id =  'ut_user_0000003')"
qr_filter.exec ( str_filter )

但这不是：

        str_filter = "declare @userid varchar(15) set @userid = 'ut_user_0000003' " \
                 "declare @user_region_preference varchar(max) " \
                 "set @user_region_preference = (SELECT region_pref FROM ut_users WHERE (user_id = @userid)) " \
                 "select @user_region_preference "
        qr_filter.exec ( str_filter )

如果我通过ssms直接在SQL Server上运行它，则按预期运行。 任何帮助将不胜感激。