Programmer Humor

its an sql injection attack.
its rather unlikely that it works in a modern app.

assuming this would work,
it injects a command in the sql database.

it is assumed that the app runs a sql querry with the input field as a parameter e.g.
INSERT INTO "bills" (item, ammount, tip) VALUES ("steak", "20,00 $", "content of the custom tip goes here");

the semicolon indicates the end of the querry,
so the the text would cause the app to run an unfinished querry, and then start a new querry that messes up the content of the bills table.