Question

我跟进了我最近提出的复杂的mysql问题：Show the ten first contacts that I have recieved message

现在我知道它遗漏了一些东西，我的最后一个问题是：

我想创建那个Sql语句显示我的十个第一次接触收到了来自的消息他们最新发送的消息和时间。表列是messageId，消息，fromProfileId，toProfileId，调用timeStamp和table 消息。数据库是Mysql和 Java是语言。但我想要这个发生在一个单独的sql语句中。

缺少的是我想要显示我发送的邮件，但它应该与我收到的用户收到的邮件分组：

我有十个第一次接触收到来自或发送的消息用他们最新发送的消息和时间。

理解起来有点复杂？好。这样想。上面引用的第一个sql语句只显示我从中获取的消息。但是如果我发送消息怎么办？该消息永远不会出现。

这是我的代码，但我没有成功（看看我在哪里标记了评论）：

"SELECT M2.messageProfileId, profiles.profileMiniature, profiles.firstName, profiles.lastName, profiles.timeFormat, lastMessages.message, lastMessages.timeStamp " +
            "FROM   (" +
            "       SELECT IF(M1.fromProfileId = ?, M1.toProfileId, M1.fromProfileId) AS messageProfileId, " +
            "           max(M1.timeStamp) AS lastMessageTime " +
            "       FROM messages AS M1 " +
            "       WHERE M1.toProfileId = ? " +
            "       OR M1.fromProfileId = ? " +
            "       GROUP BY IF(M1.fromProfileId = ?, M1.toProfileId, M1.fromProfileId) " +
            "       ORDER BY max(M1.timeStamp) DESC " +
            "       LIMIT 10 " +
            "       ) AS M2 " +
            "INNER JOIN messages AS lastMessages " +
            "ON     (" +
            "       lastMessages.timeStamp = M2.lastMessageTime " +
            "AND    lastMessages.fromProfileId = M2.messageProfileId" +//This to be like the if statements above, but how?
            "       )" +
            "INNER JOIN profiles " +
            "ON M2.messageProfileId = profiles.profileId ";

更新

上述代码中的所有问号都将替换为相同的ID，例如27.

更新

你现在必须解决一行问题。看看上面的注释行。我不知道如何在where子句中创建if语句？

Answer 1

好的，我自己想出来了

   "SELECT M2.messageProfileId, profiles.profileMiniature, profiles.firstName, profiles.lastName, profiles.timeFormat, lastMessages.message, lastMessages.timeStamp " +
                "FROM   (" +
                "       SELECT IF(M1.fromProfileId = ?, M1.toProfileId, M1.fromProfileId) AS messageProfileId, " +
                "           max(M1.timeStamp) AS lastMessageTime " +
                "       FROM messages AS M1 " +
                "       WHERE (M1.toProfileId = ? " +
                "       OR M1.fromProfileId = ?) " +
                "       GROUP BY IF(M1.fromProfileId = ?, M1.toProfileId, M1.fromProfileId) " +
                "       ORDER BY max(M1.timeStamp) DESC " +
                "       LIMIT 10 " +
                "       ) AS M2 " +
                "INNER JOIN messages AS lastMessages " +
                "ON     (" +
                "       lastMessages.timeStamp = M2.lastMessageTime " +
                "AND    (" +
                "       lastMessages.fromProfileId = M2.messageProfileId " +
                "OR     lastMessages.toProfileId = M2.messageProfileId " +
                "       )" +
                "       )" +
                "INNER JOIN profiles " +
                "ON M2.messageProfileId = profiles.profileId ";

SQL：我收到消息或发送的十个第一个联系人以及他们最新发送的消息和时间

1 个答案: