That's like saying "Do not drive a car with wheels." without offering any alternative means of transport.
I was meant to be generic, not specific to databases.
BUT, as said by a AC comment below, PostgreSQL is the answer. I'd say it's the obvious choice nowadays in matter of relational databases. It's free, it's fast, it's robust, it's powerful. It has a giant community support. Why in the heavens someone today would pay to be locked in the Oracle's leash?
Oracle may be evil, but *every* other vendor offering those same solutions locks in their customer in some way. And good luck practicing abstinence.
The only "vendor lock-in" in PostgreSQL is just the way it works, like the functions it supports, and not a stringent and punitive contract. You can run it the way you want it, no legal issues.
In my job, we use it in a handful of high-performance applications. Not meant to do any slashvertisement here, but we even use AWS Aurora (it's based on PostgreSQL, and has all it's benefits) and AFAIK no harsh vendor lock-in, we can migrate our data back to our PostgreSQL servers if we will. So far we are pretty happy with it.