findDialMembership's IN or just dm.user_id

[menzhessarov]

Hello again! I have so many questions. Forgive me for taking your time.

userID := wtf.UserIDFromContext(ctx)
where = append(where, '(
  d.user_id = ? OR
  dm.dial_id IN (SELECT dm1.dial_id FROM dial_memberships dm1 WHERE dm1.user_id = ?)
)')
args = append(args, userID, userID, userID)

1. Why should there be IN instead of dm.user_id = ?
2. I see only two question marks, is there a reason to append a third userID argument?