But you need to know in advance which keys/paths you want to index. Postgres can index the entire JSON document (or parts of it) and they can support unknown q

But you need to know in advance which keys/paths you want to index. Postgres can index the entire JSON document (or parts of it) and they can support unknown query condition (e.g. using a JSON path). This isn't as fast as a proper B-Tree index, but still faster than a full table scan.