If you are making use of the using block, you don't need to explicitly call Close, because that will be called as a part of Dispose for you at the end of the using block.* Calling Close on a connection object enables the underlying connection to be pooled.* Calling Dispose on a connection alleviates the need for you to call Close on it explicitly. It not only ensures that the underlying connection can be pooled, but it also makes sure that allocated resources can now be garbage collected.* Not calling either Close or Dispose will effectively kill your application performance by increasing the connection pool to a maximum limit, and then everyone will have to wait for the next available connection object. Not only that, but even when the open connection fall out of scope, they won't be garbage collected for a relatively long time because the connection object itself doesn't occupy much memory-and the lack of memory is the sole criterion for the garbage collector to kick in and do its work.In short, Dispose is the best option as it helps garbage collection and connection pooling, Close is second best option as it helps only connection pooling, and not calling either Close or Dispose is so bad that you shouldn't even go there.
定义SqlConnection conn= new SqlConnection(strConn)后，这只是赋值,实例化了类 conn.Open()//打开数据库 conn.Close()//关闭数据库 conn.Dispose()/释放conn,和conn=null是一个道理，不过这个时候是conn本身的地址也没了
这里写using是更好的控制代码
如果你没有释放conn
using自动帮你释放
是Dispose conn对象还是关闭数据库？
如果你的conn是在外面创建的资源,它不会帮你释放资源
用using在你的代码里主要是释放链节
try{}finally{}
conn.Open()//打开数据库
conn.Close()//关闭数据库
conn.Dispose()/释放conn,和conn=null是一个道理，不过这个时候是conn本身的地址也没了