In particular:

iex(1)> list_of_ids = [61, 62]
'=>'
iex(2)> IO.inspect(list_of_ids)
'=>'
'=>'
iex(3)> IO.inspect(list_of_ids, [charlists: :as_lists]) 
[61, 62]
'=>'
iex(4)> to_string(list_of_ids)
"=>"
iex(5)>

i.e. the query returned a list of two historiaclinicamedico_id values, 61 and 62 respectively.

There really isn’t enough information to give an answer. For example:

iex(1)> alias MusicDB.Track
MusicDB.Track
iex(2)> import Ecto.Query
Ecto.Query
iex(3)> album_id = 5
5
iex(4)> IO.inspect(Repo.all(from t in Track, where: t.album_id == ^album_id and not is_nil(t.id), select: t.id))

20:04:17.914 [debug] QUERY OK source="tracks" db=2.0ms
SELECT t0."id" FROM "tracks" AS t0 WHERE ((t0."album_id" = $1) AND NOT (t0."id" IS NULL)) [5]
[33, 32, 31, 30]
[33, 32, 31, 30]
iex(5)>

=> typically appears in the representation of Elixir maps where the keys aren’t atoms.

iex(5)> IO.inspect(Map.new([{"a",1},{"b",2}]))
%{"a" => 1, "b" => 2}
%{"a" => 1, "b" => 2}
iex(6)>