只選擇用戶/消息,這些消息互相關聯,你可以使用
SELECT u.UserId, u.FirstName, u.LastName, m.MessageId, m.Heading, m.Body
FROM User_Messages h
INNER JOIN User u ON h.UserId = u.UserId
INNER JOIN Messages m ON h.MessageId = m.MessageId
要選擇所有用戶(和增加他們的消息,如果有的話)使用方法:
SELECT u.UserId, u.FirstName, u.LastName, m.MessageId, m.Heading, m.Body
FROM User u
LEFT JOIN User_Messages u ON h.UserId = u.UserId
LEFT JOIN Messages m ON h.MessageId = m.MessageId
最後,選擇的消息,並添加用戶信息,他們每個人的使用:
SELECT u.UserId, u.FirstName, u.LastName, m.MessageId, m.Heading, m.Body
FROM Messages m
LEFT JOIN User_Messages h ON h.MessageId = m.MessageId
LEFT JOIN User u ON h.UserId = u.UserId