SQL Query with variables

I am fairly new to WordPress and I like its capabilities but I am not sure how to run custom SQL queries:
I have a simple database table Tradespeople, their Trade, a Phone Number and an Email. I have created a template page which runs two queries, a distinct select of Trades and then a Select All list of all fields. I have the Distinct resultset at the top and what I want to do is allow users to select one of the Distinct results and then re-run the Select All based on their selection. Is this do-able?

Thanks
Jonathan