GPL closed source web application?

Question

Licenses for software and other works

To write a project in Java EE, you need MySQL on the server side, neo4j - they are under the GPL. On the client side for Android, iOS, Windows platforms - SDL2, which is under zlib, at the same time emscripten - under mit
zlib and mit do not require opening the source code, but with the GPL, as far as I know, not everything is so simple.

• Does the GPL require all source code to be open source, or can only parts of it be?
  
• If I don't want to open source (neither from the client side nor from the back end) then do I have to buy a commercial license for basic use of MySQL?
  
• What would it be like to provide the source code partially, or with errors, so that "some" could not collect it all and profit from it
  

Answer 1

Simple use of MySQL does not require disclosure of source code .
With neo4j, everything is a little more complicated , but the solution is immediately offered - to interact with neo4j via HTTP REST.