虽然已经解决，但很想知道原因!
private void Page_Load(object sender, System.EventArgs e)
{
// 在此处放置用户代码以初始化页面
if (Request.Params[ "Id "] != null)
{
itemId = Int32.Parse(Request.Params[ "Id "]);
}
if (itemId != 0)
{
OleDbConnection objConn=new OleDbConnection( "Provider=Microsoft.Jet.OLEDB.4.0; Data Source= " +
Server.MapPath( "../mydatabasermvb.mdb "));
string SQL= "select * from [news] where id like ' "+itemId + " ' " ;
OleDbDataAdapter objCommand=new OleDbDataAdapter(SQL,objConn);
DataSet ds=new DataSet();
objCommand.Fill(ds, "news ");
this.DataGrid1.DataSource = ds.Tables[ "news "].DefaultView;
this.DataGrid1.DataBind();
string SQL= "select * from [news] where id like ' "+itemId + " ' " ;这一句用like就可以显示出来而string SQL= "select * from [news] where id= ' "+itemId + " ' "
就数据库为空。第一次提问，谢谢大家
[解决办法]
id是整型就应该这样写
string SQL= "select * from [news] where id= " + itemId
如果是string就没必要这样
itemId = Int32.Parse(Request.Params[ "Id "]);
转型了
，如果是string
string SQL= "select * from [news] where id like ' "+itemId.Trim() + " ' " ;//把两边空字符去掉
