Perhaps my wording was unclear - I'm not talking about postgres' efficiency, but efficiency of processing the data that postgres produces. Consider the example

Perhaps my wording was unclear - I'm not talking about postgres' efficiency, but efficiency of processing the data that postgres produces. Consider the example of an ORM that's storing an object with three multi-valued properties on the object it's encoding, each with 100 values. Encoding one has a row with three arrays in it, encoding two is the result set from joining to separate tables. In the end, it's quite plainly obvious that it's going to be cheaper (and, frankly, easier) to construct the object from a row with three arrays of size 100 in it than it is from a million row result set. Yes, this is absolutely a corner case (particularly with many multi-valued props of such a cardinality), but I'm not really sure why it requires numbers to prove - unless there's some kind of JDBC/ODBC technique for dealing with this situation that I'm simply unaware of?