End-to-end encrypted databases — that allow encrypted data to be processed without the decryption keys — are an intermediate design point before practical fully-homomorphic encryption (FHE).

Whether in-the-cloud or on-premise there is a shift to a model where individual applications need to protect themselves instead of relying on firewall-like techniques. That goes especially for the interaction between applications and storage engines, and between applications and databases.”
— Werner Vogels, Amazon.com CTO

CryptDB is a system that provides practical and provable confidentiality for applications backed by SQL databases. It works by executing SQL queries over encrypted data using a collection of efficient SQL-aware encryption schemes.

CryptDB is the first practical system that can execute a wide range of SQL queries over encrypted data. The key insight that makes our approach practical is that most SQL queries use a small set of well-defined operators, each of which we are able to support efficiently over encrypted data.”
— Ada Popa, Redfield, Zeldovich, and Balakrishnan