Use dropdownlist to show data

Hi every one

I have 2 Dropdownlist  and 1 datalist in my page I bind my datalist from DB that show some product when pageload.

I have 2 Table in my Database

1-Customer Table

2-Product Table 

Column Behcode is same in these table with this column I can see which products are for customer

In my first DDL show city name in second DDL show Shoppingcenter data

I want when user click on City dropdownlist and after that select her Shopping center it show product from product table that have that value from customer table.

how i can do it?