数据库应用:无法更新到数据库

下列代码去掉注示行后出错,无法在DataSet中更新数据,不知为什么?????????????????????

string myConnection="user id=sa;password=toney;initial Catalog=TestDB;Data Source=localhost";
string mySelectQuery="select * from company";

SqlConnection myConn = new SqlConnection(myConnection);
SqlDataAdapter myDataAdapter = new SqlDataAdapter();
myDataAdapter.SelectCommand = new SqlCommand(mySelectQuery, myConn);
SqlCommandBuilder cb = new SqlCommandBuilder(myDataAdapter);
myConn.Open();

DataSet ds = new DataSet();
myDataAdapter.Fill(ds, "company");

//ds.Tables["company"].Rows[0]["companyip"]="202.11.62.99";

myDataAdapter.Update(ds, "company");
myConn.Close();