MySQL (the same as most of the traditional SQL databases) is not decentralised. It can distribute data among different servers but they should be preconfigured and some of them will have more power than others (usually one or two "master" servers).

Blockchain is on the other hand a "database" that stores copy of data on the computers of all clients (nodes) and has mechanics needed to accept simultaneous writes and synchronise data between nodes.

Technically blockchain is much more difficult to setup and develop upon than centralised databases, so better to avoid using it unless you have a strong reasoning and knowledge.