You could take this even further and add triggers to see if your move is legal or not. Or delete row with a conflict when you capture a piece.
At the scales these games operate, enterprisey oracle clusters start to look like a pretty good solution if you don't already have some custom tech stack that perfectly solves the problem.
I've always wondered what kind of stack games like EverQuest were built on.
The game servers are all C++ and don't use stored procedures for general gameplay management. They do handle inventory management so that item duping is generally not possible, and complex things like cross-server character transfer use stored procedures.