Access导出xml

数据库中有多个表，eg，SMT_Folder_Table，SMT_Object_Table，SMT_Control_Table等，关系是：SMT_Object_Table.ParentID=SMT_Folder_Table.ID,  SMT_Control_Table.ParentID=SMT_Object_Table.ID
怎样写sql语句，将这三个表中的内容读出来写成想xml文件？

现在我的代码是这样的
C# code:

DataTable dt = new DataTable();
using (OleDbConnection conn = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + @"E:\Project\Copy of SmartTesterNet\SmartTesterNet.Web\App_Data\MR_System_All.mdb"))
{
try
{
OleDbCommand cmd = new OleDbCommand("select * from SMT_Folder_Table,SMT_Object_Table where SMT_Object_Table.ParentID =SMT_Folder_Table.ID", conn);
OleDbDataAdapter oda = new OleDbDataAdapter(cmd);
oda.Fill(dt);
dt.TableName = "SMT_Folder_Table";
cmd.Dispose();
}
catch (Exception ex)
{
conn.Close();
throw new Exception(ex.Message);
}
}

dt.WriteXml(@"E:\Project\Copy of SmartTesterNet\SmartTesterNet.Web\App_Data\123.xml",true);



得到的结果是以下格式
XML code

---

Cod