SqlConnection conn = new SqlConnection();
conn.ConnectionString = "Data Source=LIYONGPING;Initial Catalog=BookShop;User ID=sa;Password=2008aozheng@))^";
//创建命令对象
SqlCommand selectCmd = new SqlCommand();
selectCmd.CommandText = "select * from Books";
selectCmd.Connection = conn;
//设置数据适配器的SelectCommand属性
da.SelectCommand = selectCmd;
//创建数据集对象
DataSet data = new DataSet();
//使用数据适配器填充数据集
da.Fill(data, "Books");
//将数据显示在页面的GridView控件上
GridView1.DataSource = data.Tables["Books"];
GridView1.DataBind();
selectCmd.CommandText = "select * from Books";怎么判断这句话查询出来的是空