//1   连接字符串
            string connectionString
                = "server=127.0.0.1;integrated security=true;database=MSPetShop4";
            // = "server=.;uid=sa;pwd=SQL@5;database=AdventureWorks2012";
            // = "server=.;user id=sa;password=SQL@5;database=AdventureWorks2012";
            //2 实例化数据库连接
            using(System.Data.SqlClient.SqlConnection connection = new SqlConnection(connectionString))
            {
                //定义执行SQL语句,可以为select查询,也可以为存储过程,我们要的只是返回的结果集.
                string sql = "SELECT 客户,产品,年龄 FROM dbo.A";

                //强大的SqlDataAdapter 
                System.Data.SqlClient.SqlDataAdapter adapter = new SqlDataAdapter(sql,connection);

                DataSet ds = new DataSet();
                //Fill 方法会执行一系列操作 connection.open command.reader 等等
                //反正到最后就把 sql语句执行一遍,然后把结果集插入到 ds 里.
                adapter.Fill(ds);

                DataTable dt = ds.Tables[0];
            }
            Console.ReadLine();