Most PHP applications do fundamentally the same thing: Shuffle data from an SQL database to a web page and back again. The details vary with the application, but in general that's what most web apps do. That very quickly runs into the bane of most PHP developers' lives: SQL syntax.
It's not SQL syntax itself that is bad per se. The problem is that it is a string-serialized format, which means you have to take your nice clean data structures and serialize them out into a string that has no semantic meaning to your PHP application. That's boring, dull, and introduces all sorts of places to totally mess up your application with a typo, and that's without even touching on issues of security. And then there are the issues with SQL syntax itself, in particular the way in which INSERT and UPDATE statements, which seem like they should be similar, have no similarity whatsoever. That makes "replace" operations (insert if new or update if not) very tedious to write, particularly if you have a lot of fields.
Fortunately, with a little ingenuity and help from PHP's array handling, we can give ourselves a common syntax for INSERT and UPDATE operations that maintains semantic meaning, and then get DELETE statements free of charge. Let's see how.