Events Dynamic Dropdown

I have an Events Database. It has 3 tables. First main table contains the ID, Date, Event Name and Category. Second table contains the ID and Date, the fields are ie 3rd July, 4th July etc. - this feeds the date column of the first main table. Third table contains the ID and Category, the fields are ie Music, Family etc. - this feeds the category column of the first main table. I would like two search dropdown lists (Date and Category) that would filter the list upon selection ie. if someone selects the 3rd of July that it would only show the categories from that date, this would then show the filtered results on same search page.

I have used datassist to create the Search and Results page:

search.php

I have Dynamic Dropdown plugin but I just don't know how to use it to create this type of filtered menu and results.

I have attached database.

I have very little PHP knowledge.

Thanks for any help in advance.