通过参数传递数据类型来更改表会导致语法错误

我正在使用Visual Studio创建一个程序。在这个程序中，我必须查找所有创建的表，看看列表中是否存在一列，如果不创建的话。为此，我创建了以下变量：

Dictionary<string, List<Dictionary<string, string>>> TABLE_DICT //the string saves the name of the table, the list the columns and types
List<Dictionary<string, string>> TABLE_LIST = new List<Dictionary<string, string>>(); //list of columns in a table with its type
Dictionary<string, string> DICT = new Dictionary<string, string>(); // name of column and the type of this column

代码如下：

try
            {
                conn = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + DBstring);
                conn.Open();
                foreach (KeyValuePair<string, List<Dictionary<string, string>>> TABLE_kvp in TABLE_DICT)
                {
                    foreach (Dictionary<string, string> dic in TABLE_kvp.Value)
                    {
                        foreach (KeyValuePair<string, string> kvp in dic)
                        {
                            DataTable dt = conn.GetSchema("Columns", new string[] { null, null, TABLE_kvp.Key, kvp.Key });
                            if (dt.Rows.Count == 0)
                            {
                                OleDbCommand command = new OleDbCommand();
                                command.Connection = conn;
                                command.CommandText = "ALTER TABLE ? ADD COLUMN ? ? ";
                                command.Parameters.AddWithValue("@tablename", TABLE_kvp.Key);
                                command.Parameters.AddWithValue("@col", kvp.Key);
                                command.Parameters.AddWithValue("@val", kvp.Value);
                                command.ExecuteNonQuery();
                                command.Connection.Close();
                            }
                        }
                    }
                }
            }
            catch (OleDbException ex)
            {
                ErrorForm ef = new ErrorForm(ex.Message, this.BackColor);
                ef.ShowDialog(this);
            }

问题是，即使我更改以下stll的命令文本时出现语法错误，代码也会捕获语法错误的异常：

command.CommandText = "ALTER TABLE ? ADD COLUMN [?] ? NULL";
command.CommandText = "ALTER TABLE ? ADD COLUMN [?] ?";
command.CommandText = "ALTER TABLE [?] ADD COLUMN ? ? ";
command.CommandText = "ALTER TABLE ? ADD COLUMN ? MEMO ";

在谷歌上搜索，至少是列表的最后一个，不必出错，或者这是我相信的，但仍然会出错。知道吗？

var validator = new Regex(@"^'w+$");
if (new[] { TABLE_kvp.Key, kvp.Key, kvp.Value }.All(validator.IsMatch))
{
    command.CommandText = String.Format("ALTER TABLE {0} ADD COLUMN {1} {2}", 
        TABLE_kvp.Key,
        kvp.Key,
        kvp.Value);   
}