C#&Oracle winform向数据库中插入时间

//SQLString = $"insert into A_DTST2 values({BeginTime},8,9)";//缺失逗号
                    //SQLString = "insert into A_DTST2 values(啥玩意,8,9)";//列在此处不允许
                    //SQLString = "insert into A_DTST2 values('啥玩意',8,9)";//System.InvalidOperationException:“集合已修改；可能无法执行枚举操作。”
                    //但能添加
                    //SQLString = "insert into A_DTST2 values('what',8,9)";//能添加
                    //String str = "哼";
                    //SQLString = $"insert into A_DTST2 values({str},8,9)";//列在此处不允许
                    //String str = "what";
                    //SQLString = $"insert into A_DTST2 values('{str}',8,9)";//列在此处不允许，也许是单引号双引号的问题。就是，外层+单引OK了
                    //DbHelperOra.ExecuteSql(SQLString);