Ajax 3 levels dynamic dropdown

I have four table in database 1. Countries 2. Stats or Provinces 3. Cites 4. Branches or offices now i want to populate all branches in HTML Table List filtered by three drop-downs lists

For Example:

1. If i'm going to select [ United Stats ] from [ 1st Country Dropdown list ] than 2nd dropdown of stats shows all stats of the above selected country via ajax e.g New York, Wasongton e.t.c

2. than if I select [ Washington ] from [ 2nd Stats Dropdown list ] than 3rd dropdown of cities shows all cites of the above selected stat via ajax e.g Asotin, Bellingham, Everett , e.t.c

3. than if I select [ Bellingham ] from [ 3rd Cities Dropdown list ] than all officies of Bellingham shows in a HTML Table list.

any one have idea, link, article, tutorial or any thing which is helpful in this regard will be appreciated