验证数据是否重复

Question

while (myDataReader.Read())
            {
                if (myDataReader.GetValue(0) == IDTextBox.Text)//这里是否有错误？
                 {
                    Response.Write(myDataReader.GetValue(0));
                     Response.Write("<script language='javascript'> alert('已有该图书证号！')</script>");
                     myDataReader.Close();
                     break;
                 }
            }

Answer 1

while (myDataReader.Read()) 
{ 
　　string str = myDataReader.GetString(0);
   if (str == IDTextBox.Text) 
   { 
     Response.Write(str);
     Response.Write(" <script language='javascript'> alert('已有该图书证号！') </script>"); 
     myDataReader.Close(); 
     break; 
   } 
}