Why Banks or Financial Companies prefer Oracle than other RDBMS for their "Core" systems? [closed]
Oracle has a reputation for better reliability and security. Historically, it has outperformed and out-scaled any other SQL engine. This is changing, but the perception is still there. In many markets, Oracle is still perceived as the gold standard. Financial services seems to be one of them.
Corporate Culture... History... Bias...
AND Oracle is a very good DB, but so are plenty of others these days.
However, if the financial institution has been around forever, and they've used Oracle forever (since it WAS once in a class of its own), there's an investment there.
Also, since Oracle once dominated this market, people with experience in these industries are already more likely to be familiar with it and comfortable with it, so when building a new system it's a "comfortable" choice.
PostgreSQL is also used, Caixa (a large bank in Brazil) uses it:PostgreSQL in Mission-Critical Financial Systems