excel表中有大约三万条记录，每次都从excel中查询费时较长，读入内存 再用linqtodatatable进行过滤查找 

   private void button2_Click(object sender, EventArgs e)
        {



            string excelFilePath = @"C:\dd.xls";
            string excelSheetName = @"medpinyin";
             tb = GetExcelTableByOleDB(excelFilePath, excelSheetName);
        }
        private void button4_Click(object sender, EventArgs e)
        {
            EnumerableRowCollection<DataRow>kk =
                tb.AsEnumerable().Where(A => A.Field<string>("medpy").StartsWith("ZYMP"));
            ArrayList al = new ArrayList();
            foreach (var q in kk)
            {
                if (!al.Contains(q["medname"].ToString()))
                {

                    al.Add(q["medname"].ToString());
                }
            }
            string[] s = (string[])al.ToArray(typeof(string));
            MessageBox.Show(s[0]);
            MessageBox.Show(kk.Count().ToString());
        }
        /// <summary>
        /// 读取Excel中数据
        /// </summary>
        /// <param name="strExcelPath"></param>
        /// <param name="tableName"></param>
        /// <returns></returns>
        public static  DataTable GetExcelTableByOleDB(string strExcelPath, string tableName)
        {
            try
            {
                DataTable dtExcel = new DataTable();
                //数据表
                DataSet ds = new DataSet();
                //获取文件扩展名
                string strExtension = System.IO.Path.GetExtension(strExcelPath);
                string strFileName = System.IO.Path.GetFileName(strExcelPath);
                //Excel的连接
                OleDbConnection objConn = null;
                switch (strExtension)
                {
                    case ".xls":
                        objConn = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + strExcelPath + ";" + "Extended Properties=\"Excel 8.0;HDR=yes;IMEX=1;\"");
                        break;
                    case ".xlsx":
                        objConn = new OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + strExcelPath + ";" + "Extended Properties=\"Excel 12.0;HDR=yes;IMEX=1;\"");//此连接可以操作.xls与.xlsx文件 (支持Excel2003 和 Excel2007 的连接字符串)  备注： "HDR=yes;"是说Excel文件的第一行是列名而不是数，"HDR=No;"正好与前面的相反。"IMEX=1 "如果列中的数据类型不一致，使用"IMEX=1"可必免数据类型冲突。 
                        break;
                    default:
                        objConn = null;
                        break;
                }
                if (objConn == null)
                {
                    return null;
                }
                objConn.Open();
                //获取Excel中所有Sheet表的信息
                //System.Data.DataTable schemaTable = objConn.GetOleDbSchemaTable(System.Data.OleDb.OleDbSchemaGuid.Tables, null);
                //获取Excel的第一个Sheet表名
                // string tableName1 = schemaTable.Rows[0][2].ToString().Trim();
                string strSql = "select * from [" + tableName + "$]  ";
                //获取Excel指定Sheet表中的信息
                OleDbCommand objCmd = new OleDbCommand(strSql, objConn);
                OleDbDataAdapter myData = new OleDbDataAdapter(strSql, objConn);
                myData.Fill(ds, tableName);//填充数据
                objConn.Close();
                //dtExcel即为excel文件中指定表中存储的信息
                dtExcel = ds.Tables[tableName];
                MessageBox.Show(dtExcel.Rows.Count.ToString());
                return dtExcel;
            }
            catch (Exception ex)
            {
                //Console.WriteLine(ex.Message + "\r\n" + ex.StackTrace);
                MessageBox.Show(ex.Message + "\r\n" + ex.StackTrace);
             
                return null;
            }
        }