mysql - geographic database structure -

I have a geographical DB in mysql with more than 15m records so far every record has a field Parent_id : For example in Tuscany Italy has parent_id . It is a tree, but it is garbage

Unfortunately this

get all the leaves for all the nodes

Get all the descendents of the node

Receive immediate children of nodes

1 and 2 can be obtained with nested set structure, 4 actual With the structure. I do not know how to deal with the third

Unfortunately the nested set structure is not able to add and add nodes.

So here's the question:

1. How do you get it structured?
2. Will you keep using mysql? Something better?
3. Have you not given any advice about moving the actual DB into the new one?

In addition, DB Infos must also be through this flexible checker, do you think it is better to build and structure DB directly? if so, how?