用C#在一个已有的access数据库中db1的表HNC中添加一列(符号)无法实现,为什么?

[mjm_77]

哪位大侠帮我看看为什么这个添加列不能实现?FilePath2为文件的路径,准备在表(HNC)中添加一列(符号).
String conString1="Provider=Microsoft.Jet.OLEDB.4.0;Data Source="+FilePath2; 　　　　　　OleDbConnection aConnection = new OleDbConnection (conString1);
aConnection.Open();

OleDbCommand aCommand = new OleDbCommand ( "select * from HNC",aConnection);
OleDbDataAdapter thisAdapter=new OleDbDataAdapter("select * from HNC ",aConnection);

DataSet thisDataSet=new DataSet();
DataTable dtData=new DataTable("HNC");
thisAdapter.Fill(thisDataSet,"HNC");

dtData=thisDataSet.Tables["HNC"];
DataColumn newColumn;
newColumn=dtData.Columns.Add("符号");
newColumn.DataType=System.Type.GetType("System.String");
newColumn.AllowDBNull =true ;
newColumn.Unique = false;

thisAdapter.Update(thisDataSet,"HNC");

aConnection.Close();
感觉应该可以实现添加列,但是就是不行啊?