高手指点一下：运行以下代码后，弹出修改成功的对话框，但是数据库中的数据没有改变，为什么呢？
但是我把@g_no改成确定值后，能够改变数据库中的数据！

OleDbConnection myconnup = new OleDbConnection(connectionString);
OleDbCommand mycmdup = myconnup.CreateCommand();

mycmdup.CommandText = "update table set g_name=@g_name where (g_no=@g_no)";
mycmdup.Parameters.Add("@g_no",System.Data.OleDb.OleDbType.Char);
mycmdup.Parameters.Add("@g_name",System.Data.OleDb.OleDbType.Char);
mycmdup.Parameters[0].Value = textBox1.Text;
mycmdup.Parameters[1].Value = textBox2.Text;

try
{
myconnup.Open();
mycmdup.ExecuteNonQuery();
myconnup.Close();
MessageBox.Show("修改成功！");
}
catch{MessageBox.Show("修改失败！");}

看看这个例子：
SqlDataAdapter catDA = new SqlDataAdapter("SELECT CategoryID, CategoryName FROM Categories", nwindConn);

catDA.UpdateCommand = new SqlCommand("UPDATE Categories SET CategoryName = @CategoryName " +
"WHERE CategoryID = @CategoryID" , nwindConn);

catDA.UpdateCommand.Parameters.Add("@CategoryName", SqlDbType.NVarChar, 15, "CategoryName");

SqlParameter workParm = catDA.UpdateCommand.Parameters.Add("@CategoryID", SqlDbType.Int);
workParm.SourceColumn = "CategoryID";
workParm.SourceVersion = DataRowVersion.Original;

DataSet catDS = new DataSet();
catDA.Fill(catDS, "Categories");

DataRow cRow = catDS.Tables["Categories"].Rows[0];
cRow["CategoryName"] = "New Category";

catDA.Update(catDS);