How to write a recursion on children?

Question

MySQL

A simple example. There is such a hierarchy: region, city, regions.
The table looks like this:
Google Tab
I want to filter by State and Region. respectively in the table more than 50000 records. For a faster selection, I decided to assign all cities and regions to their regions.
code_level is the id of the hierarchy 1 - region, 2 - cities, 3 - regions, respectively.
1) I don’t know how to write a recursive function correctly to go to the very regions and visit the regions for cities and regions.
Working in Symfony2 + postgreSQL Just in case someone knows how to do this via Php.

Answer 1

"Objectively"
https://github.com/Atlantic18/DoctrineExtensions/b...
"Functionally"
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