See above but some additional points:

Keys are not stored in the database or in the application. Every data key is derived at query time via a 2-party system: 1. by the key server which manages root-key material (stored in an HSM or traditional KMS) 2. keys derived via a user credential at the time of the query

SQL Injection case: An adversary signs up to your app, pulls of a SQLi and you might think that the app will just decrypt the values. It won't because the adversary's auth cred can't derive keys to decrypt anything but the data they are explicitly allowed to access.

RCE/shell compromise: Because keys are derived on demand these kinds of attacks are largely inert. If the attacker could read memory from the running app on-demand then they could conceivably see credentials in flight but each key only ever decrypts one value so the blast radius is limited.

On the cost of decryption: Queries typically only return a subset of the values in a table and, importantly, don't need to decrypt anything at all. Querying and decryption are independent. If you DO need to decrypt a large volume of data, CipherStash can do it at 10,000 values per second.

Query performance is under 1ms for simple queries and no-more than 200-300ms for more complex queries.

Full benches here: https://github.com/cipherstash/benches

No security tool is perfect, nor "gold plated" but this tech meaningfully reduces blast area of attacks, makes many attacks inert and gives you an incredibly reliable audit trail.