I think it will depend on what you want to know.
I used Oracle Database 10g Express Edition as a data warehouse for personal / educational software projects. On the Oracle website:
Oracle Database 10g Express Edition (Oracle Database XE) is an entry-level database with a small database size based on the Oracle Database 10g Release 2 database, which is free to develop, deploy and distribute; fast loading; and easy to administer.
For what I need, I found it quick and easy to use.
Graham
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