while (reader.Read())
            {
                string assetid = reader["AssetID"].ToString();
                string assetname = reader["AssetName"].ToString();
                string str = assetid + " " + assetname;
                cboxSearchAsset.Items.Add(str);
            }

DataView dv = new DataView(tbAssetList);
  dv.RowFilter = string.Format("AssetID LIKE '%{0}%'",cboxSearchAsset.Text);
  datagridAssetList.DataSource = dv;

DataView dv = new DataView(tbAssetList);
  dv.RowFilter = string.Format("AssetID LIKE '%{0}%' AND AssetName LIKE'%
  {0}%'",cboxSearchAsset.Text);
  datagridAssetList.DataSource = dv;