To expand on what static said, in most Western nations, IP law is written so that anything developed for a company by its employees belongs to that company. Same with any data gathered for that company.
In fact, if you live in the US, by taking your ex-company's database and trying to get it hacked, you are actually breaking multiple federal IP laws, up to and possibly including the DMCA. Admittedly, the laws typically aren't enforced over things like this, but you still need to be aware.
On top of that, by publishing that database file, you've made public any data that happens to be contained inside it. I haven't bothered to open it, so I don't know what's inside it, but based on the name, the data inside could make your ex-company very, very cranky.
If your ex-company wants into it, tell them to hire a contractor or specialist.
If you want to build your own copy, then start from scratch and do it yourself.
And if you just want the data that's inside, you're on your own.