连接Access数据库：
<appSettings>
<add key="accessCon" value="Provider=Microsoft.Jet.OLEDB.4.0";Data Source=|DataDirectory|db_access.mdb"/>
</appSettings>
string con_access=ConfigurationManager.AppSettings["accessCon"].ToString();
连接SQLServer
<appSetting>
<add key="sqlCon" value="Data Source=(local);Database=数据库名称;Uid=sa;Pwd=密码"/>
</appSetting>
string con_sqlserver=ConfigurationManager.AppSettings["sqlCon"].ToString()