Clojurians Log v2

I'm trying to make a query which allows me to find all entities with a specific cardinality many attribute where that entity has more than one value for that attribute. Is there a way to do this query without resorting to sub-queries which tank my performance? e.g.

(q '[:find ?e
     :in $
     :where
     [?e :many-item ?i1]
     [?e :many-item ?i2]
     [(not= ?i1 ?i2)]])

Is it safe to open a db with a different schema than it was created with if there's data inside it? Specifically, adding new fields which were not previously inserted into? Or would I need to open two dbs with different schemas, then load the datoms from one into the other?