SQL Export after 50 entries and then Delete the Table entries entirely

this is my first post. I have insert form using pdo, ajax and sql and I Want to after 100 entries export to csv in back up folder . And then purge the table of all information. I need help to understand how I can do this? I was thinking a trigger or event or maybe C# program to do this but i wanted opinions on all things security, functionality and different ideas to make this happen. I truly do appreciate any time spent considering my request. . . Thank you