[Using Multiple Form Select Elements Sync together]

I have a list of students entered into a mysql table using the following fields:

id, name, surname, address, towncode, streetcode,

 

Another two tables has been designed so to normalize the schema:

One is the Streets table

streetcode, streetname, towncode

 

.. and the other one is towns with the following fields:

towncode, townname

 

Now i need to design a form using php to filter students depending on the town (I select using the SELECT element of a form) , and as well on the street (I select using the SELECT element of a form) which fall under that town.

 

Can someone help me out with this issue.

 

Sorry but I am new to PHP!!!!!!!