您无需添加引用，只需添加using语句即可.

 使用 System.Data.SqlClient； 

然后您可以通过SqlConnection 对象进行连接，依此类推.

add reference for sqlserver2008 in visual studio 2008?

You don''t need to add a reference, just the using statement.

using System.Data.SqlClient;

You can then connect via SqlConnection objects, and so forth.