This will be an unusual suggestion, but I highly recommend Geographic Databases and Information Systems by Stefanakis. The book is split into three parts, and t

This will be an unusual suggestion, but I highly recommend Geographic Databases and Information Systems by Stefanakis. The book is split into three parts, and the last one is specific to GIS. The other two, however, are a great introduction for databases, indices, data structures and even some graph theory. I've revisited several concepts I'd seen before at college.