If you are interested to become an Oracle expert the best place to educate yourself is www.oracle.com.

For non commercial use many Oracle products are freely available.

Expect to invest a lot of time to become comftable with using Oracle products.

Oracle database [1] is a great choice if you need to use a commercial database. For an OLTP[2] application everyone else is behind Oracle.

Look at

“Figure 1. Vendors’ Product Scores for the Traditional Transactions Use Case”

found in the Gartner report [2].

[1] https://www.oracle.com/database/index.html

[2]  https://www.gartner.com/doc/reprints?id=1-3JQ1Y2V&ct=161011&st=sb

[3] https://en.wikipedia.org/wiki/Online_transaction_processing