datareader

• Returns metadata about each column in a table , and the datareader columns that are returned , vary depending on which data provider you use
  返回有关表中每一列的元数据的顺序以及返回的datareader列会因您使用的数据提供程序而不同。
• Results are returned as the query executes , and are stored in the network buffer on the client until you request them using the
  查询结果在查询执行时返回，在并存储在客户端的网络缓冲区中，直到您使用datareader的read方法对它们发出请求。