[英]Show rows with at least one occurrence in a relation table?
我有以下表架構:
user (id, name, alias, password, active, mail, age)
comment(id, news(FK), user(FK), text, date)
new_cat(news(FK), category(FK))
我正在嘗試選擇所有評論過至少一個new
的每個category
的用戶。
這就是我沒有成功的嘗試:
SELECT * FROM user AS u, comment AS c
WHERE u.id = c.user AND c.news IN (SELECT news FROM new_cat);
我相信這沒有正確迭代並檢查每個category
,只是檢查條件是否僅適用於一個category
。
我怎樣才能正確地做到這一點?
加入表,按用戶分組並在HAVING
子句中設置條件。
如果有一個存儲所有類別的category
表:
SELECT u.*
FROM user u
INNER JOIN comment c ON c.user = u.id
INNER JOIN new_cat n ON n.news = c.news
GROUP BY u.id
HAVING COUNT(DISTINCT n.category) = (SELECT COUNT(*) FROM category);
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