vs 2005 asp.net C#修改密码界面

OleDbCommand cmd = new OleDbCommand("select * from db_Login where username='" + textBox1.Text.Trim() + "'and mm='" + textBox2.Text.Trim() + "'", conn);
if (null != cmd.ExecuteScalar())
{
if (textBox4.Text.Trim() == textBox3.Text.Trim())
{
cmd.CommandText = "Update db_Login set mm=" + textBox3.Text.Trim() + "where username="+testBox1.Text.Trim() ;
DataSet ds = new DataSet();
OleDbDataAdapter Myadapter = new OleDbDataAdapter(cmd.CommandText, conn);
Myadapter.Fill(ds);
}
else
{
return;
}
}
else
{
MessageBox.Show("请输入正确的用户名和密码！");
}