"basically i want to make an app that gets all missing values from target database to the main database. How to achieve this i have no idea.By searching on net i just can get names of tables and queries."
Ouch! This is not a simple task, and it requires a lot of thinking and some planning in the database design. It's not as simple as "Find all records in this DB that aren't in that DB and insert them" - it's a lot more complex, as the updates normally have to cope with data in both directions, and record deletes, updates, and so forth.
You need to start by look at
Database Replication[
^] - follow a couple of the links to get a feel for how complex a system you need, and then start reading in depth as to how to design for it and add it to your system. But - work with backups of your DB, and don't expect this to be a ten minute operation! :laugh: