文档:Closing the connection is done using end() which makes sure all remaining queries are executed before sending a quit packet to the mysql server.所以,调用了end()不会马上关闭连接,要等剩余的查询执行完才关闭,该触发的回调还是触发。destroy()才是直接关闭连接。具体实现就是把全部操作都放到队列里执行,end()只是把一个Quit操作放入队列,Quit操作执行完之后才真正关闭。