我有三张桌子:人,消息和朋友。现在我需要向每个拥有相同数量的朋友并发送消息的人展示。
人拥有每个人的信息,最重要的是电子邮件。消息有一个名为“fromemail”的列,它显示发送消息的人,并且还有一个“email”列,该列引用了表人。
你可以尝试类似的东西:
SELECT p1.email, p2.email
FROM
(SELECT email, count(message_id) m_count, count(friend_id) f_count
FROM
person p
JOIN message m ON p.email = m.email
JOIN hasfriend f ON p.email = f.email) p1,
(SELECT email, count(message_id) m_count, count(friend_id) f_count
FROM
person p
JOIN message m ON p.email = m.email
JOIN hasfriend f ON p.email = f.email) p2
WHERE
p1.email = p2.email AND
p1.m_count = p2.m_count AND
p1.f_count = p2.f_count;