Many thanks in advance to all who offer help.

Yep, yet another newbie question. So new to php it is causing a real headache

On my webpage i currently have two drop down boxes for user selected options where the selection comes from different MySql tables. The first box display ok, without any issue, but the second will not as when the page is first loaded, the variable being used to define the selection is blank as the first box has not been chosen.

How to refresh the page or do whatever is necessary, so that when the user choses their selection form the first drop down, then that choice can be used to define the WHERE element of the mysql query.