What third-party database is being used?
SQL Developer suports migration from a few...
SQL Server 2008
Did you translate all the SQL Server statement to Oracle SQL Syntax?
Did you rebuild all the methods so that they use Oracle Best Practice? (SQL Server "Best Practices" are usually Oracle's "Worst Practices", and vica-versa)
You are aware that Oracle has defaulted to READ COMMIT (and uses MVCC) since version 4? AFAIK - SQL Server just recently started offering MVCC capability
The way you handle a Transaction is different between the two servers. Did you re-write your code so that it take advantage of Oracle's MVCC? hint Oracle doesn't do "dirty data" (except in 2-phase commits)
SQL Server and Oracle have different features/capabilities. Some features/capabilities of SQL Server may need to be written in Oracle. Oracle may have features/capabilities that makes some SQL Server code totally worthless.
Did you review your code and optimize it to use Oracle features/capabilities?
Transferring the data from one server to another is easy.
Migrating the code isn't.
Remember: Database Agnostic Code is a Myth
Tell me how to export a finished database from ms sql to Oracle so as not to fill it again?
I’m doing the transfer for the site https://mirpokera.com.ua/ua/. Written in php. Could this be difficult or platform is not important?
What is a "finished" database?
What do you mean by "so as not to fill it again"?