I've implement an interesting service 15 years ago. Recently I've heard of it.

So this service was basically an "universal integration service". Company wanted to share some data, and they wanted to implement it in an universal way. So basically I've implemented SOAP web service which received request with SQL text and responded with list of rows. This service was surprisingly popular and used a lot.

I was smart enough, so I built a limited SQL syntax parser and UI, so administrator could just set up tables and columns they wanted to share for this specific client. SQL query was limited in a sense that it worked only with one table, simple set of columns and some limited conditions (that I bothered to implement).

The reason I've heard about it few months ago is that they shared with me, that they caught a malicious guy, who worked at some company integrating with this system and he tried to do SQL attack. They noticed errors in the logs and caught him.

Their database is pretty much done and frozen, regarding to schema. They hardly evolve it. So this service turned out ot be pretty backwards-compatible. And simple changes, of course, could be supported with view, if necessary.