求助。地区分类里，加区县的方法。

比如有这样的数组。
var cityArr = [
["CategoryName","ParentId","Id"],
["北京","0","1"],
["重庆","0","2"],
["上海","0","3"],
["天津","0","4"],["河北","0","5"],
["石家庄","5","101090101","S"],
["保定","5","101090201","B"],
["承德市","5","101090402","C"],
["沧州","5","101090701","C"],
["衡水","5","101090801","H"],
["邯郸","5","101091001","H"],
["廊坊","5","101090601","L"],
["秦皇岛","5","101091101","Q"],
["唐山","5","101090501","T"],
["邢台","5","101090901","X"],
["张家口","5","101090301","Z"],
]现在有三个select
第一个是”省“，第二个是对应的省”诚市“ 第三个是”区县“现在，当第一个选省时比如”河北“，第二个就调对应的 ”城市“数据提供选择，比如 石家庄，保定……等等，我的问题是：当第二个选了对应”城市“数据时，我要怎么样做，在第三个调出对应的区县。这三级联动关系的数据，我以存在数据表里，我要把数据表导成什么样的形式，Js联动代码，我应该怎样写，才能实现此功能呢，可以举一个例子不哟？？？？比如，”石家庄“ 对应的区县为 ”AB“，”AC“…………还请高手指点一下。