> why an SQL couldn't implement document storage to go along with its relational goodness? (…) Postgres's Hstore appears to offer the same advantages as a docum

> why an SQL couldn't implement document storage to go along with its relational goodness? (…) Postgres's Hstore appears to offer the same advantages as a document store, without sacrificing the ability to add relations when necessary. Where's the downside? PostgreSQL can store arbitrary unstructured documents just fine: hstore, json, … Each come with the possibility to actually index arbitrary fields within the documents using a BTREE index on an expression, and arbitrary documents wholesale using GIST index. Besides the need to know a thing or two on query optimization, the only downside I can think of is that ORMs are usually broken (Ruby's Sequel is a notable exception). But this isn't a problem with Postgres itself; it's a problem with ORMs (and training, admittedly).