It's worth pointing out that trusted execution for individual queries does not, in general, rule out the attacks discussed in this paper. If the database collects (for example) frequency information about queries, inference attacks can still be used to recover plaintext.
EDIT: The fundamental problem is that trusted hardware doesn't hide the access pattern by itself. Trusted hardware can be used to hide some kinds of access patterns, but it's highly nontrivial and has only been demonstrated in some limited settings. For example, there was a paper at NSDI this year called "Opaque" which showed how to use SGX to hide access patterns for some kinds of Spark queries.
EDIT: The fundamental problem is that trusted hardware doesn't hide the access pattern by itself. Trusted hardware can be used to hide some kinds of access patterns, but it's highly nontrivial and has only been demonstrated in some limited settings. For example, there was a paper at NSDI this year called "Opaque" which showed how to use SGX to hide access patterns for some kinds of Spark queries.