-- https://meta.discourse.org/t/68756/8?u=sidv
-- [params]
-- topic_id :topic_id = 536
SELECT u.username
FROM badge_posts p
JOIN topics t ON p.topic_id = t.id
JOIN users u ON p.user_id = u.id
WHERE t.id = :topic_id
GROUP BY p.user_id,u.username
SELECT u.username, u.name
FROM badge_posts p
JOIN topics t ON p.topic_id = t.id
JOIN users u ON p.user_id = u.id
WHERE t.id = :topic_id
GROUP BY p.user_id,u.username
…その後、以下のエラーが発生しました…
PG::GroupingError: ERROR: column "u.name" must appear in the GROUP BY clause or be used in an aggregate function
LINE 12: SELECT u.username, u.name
そこで、クエリを以下のように変更したところ、見事に動作しました!
SELECT u.username, u.name
FROM badge_posts p
JOIN topics t ON p.topic_id = t.id
JOIN users u ON p.user_id = u.id
WHERE t.id = :topic_id
GROUP BY p.user_id,u.username,u.name