How can I improve this Clojure function?

Question

I just wrote my first Clojure function based on my very limited knowledge of the language. I would love some feedback in regards to performance and use of types. For example, I'm not sure if I should be using lists or vectors.

(defn actor-ids-for-subject-id [subject-id]
  (sql/with-connection (System/getenv "DATABASE_URL")
    (sql/with-query-results results
      ["SELECT actor_id FROM entries WHERE subject_id = ?" subject-id]
      (let [res (into [] results)]
        (map (fn [row] (get row :actor_id)) res)))))

It passes the following test (given proper seed data):

(deftest test-actor-ids-for-subject-id
  (is (= ["123" "321"] (actor-ids-for-subject-id "123"))))

If it makes a difference (and I imagine it does) my usage characteristics of the returned data will almost exclusively involve generating the union and intersection of another set returned by the same function.

Answer 1

it's slightly more concise to use 'vec' instead of 'into' when the initial vector is empty. it may express the intent more clearly, though that's more a matter of preference.

(vec (map :actor_id results))