Its not happening, at least not with LLMs, maybe some future technology will be better with that, but not language models. Writing such a complex software as database engine requires strategy, awareness and rigor. It is somewhat similar to winning a sweaty game of chess with an experienced opponent. LLMs are great with broadness of their knowledge, matching patterns and synthesising that knowledge, but they fail with strategy and awareness part. And this is why they are bad in chess.