SqlConnection  sqlCon=new SqlConnection() ; 
            sqlCon.ConnectionString = "Data Source=.;DataBase=BU;Uid=sa;PWD=密码";  //.表示本机  也可以IP
           
            SqlCommand sqlStr= new SqlCommand("select  ID from A", sqlCon); 
            sqlCon.Open();

            SqlDataReader dr = sqlStr.ExecuteReader();   
            while (dr.Read())
            {
                Console.WriteLine(dr["ID"]);  //注意调用格式
            }
            sqlCon.Close();