Have you already covered the basics of loading and playing sound in p5.js? I’d suggest starting with one song if you haven’t already:
Then move to two or three songs. Once you have that, the simplest way to go to many songs is to put mp3 files in a directory, then a list of mp3 file names. That list could be stored directly in your sketch code, or it could be an external text file. No need for mysql or another database – unless you are hoping to store metadata alongside your music filenames and filter / sort the list by it, and even then you might want to just use simple tabular data like a csv file.
So, now you just need to update the text file or csv file with the song list. Keep in mind that this won’t update in a running browser tab until the tab is reloaded – unless you have the sketch code periodically reload the file resource to check for update.