Bonjour et bienvenue @rapphann 
Je ne suis pas non plus un expert en SQL Mais je pense que ce serait quelque chose comme ceci :
SELECT us.user_id, current_timestamp AS granted_at
FROM user_stats AS us
WHERE us.likes_received >= 100
AND us.likes_given >= 100
AND (:backfill OR us.user_id IN (:user_ids))