[a-dub]

it's an open area of research as far as i know. the technical terms are "private information retrieval", "private information query", "homomorphic encryption" and "secure multiparty computation."

it's some of the coolest stuff in cryptography but it also tends to be experimental or very computationally expensive. zero knowledge proofs are the simplest form i know of.

as far as i know, row level end to end encrypted databases with indices that preserve privacy do not exist yet, but i fully expect that they will.