Well, sum types are not magic - they must be stored in the memory somehow. Rust's enums tend to use a simple approach: there's a large enough integer tag (usually an 8-bit integer), followed by enough space to store any of the variants. The same exact encoding could be used with a database storage engine too.

Not sure - because in the end, a programming language also has to store this concept in memory. I don't think there is a fundamental difference.