DropDown value bind from 2 Tables

There are 2 DropDown one is "Category" other is "sub_category"

I want to show data in "sub_category" DropDown according to "category" Dropdown selected value.

But when "Category=C1" data should bind in DropDown from Database Table1 and when "Category=C2" or "Category=C3" data should bind in DropDown from Database Table2.

How to achieve this.

Please reply.