How can I improve my table design for different types of an entity? Consider an accounting system as an example. I have an Entity called Client. Client can be of different types, with different fields applicable to different types. I consider creating separate tables for different types of Client, each having fields applicable to the respective type and have one master table referencing all of them and have fields applicable to all types.

Currently, I come up with the following design:



But I don't think my design is efficient enough (or even correct and free of errors). What would you suggest? 
Also, if this is important in any way, I am planning to utilize MariaDB.
Sorry, but is an entrepreneur not also an individual? You should record the name etc. in individual, then the additional info in another table. Now you may have one person double. And stuff like address should be linked to "entity" - not even client, you may end up having suppliers there too.

The "Data Model Resource Book" has perfect diagrams for address and contact handling including relationships of entities with each other. There is a lot of detail issues you get seriously wrong in your approach.