Question

现在我正在创建一个在线游戏，我列出了最后一批玩家。

处理玩家历史的表格包含列history_join_date和history_end_date。

当填充history_end_date时，表示玩家离开了俱乐部，当它像默认（0000-00-0000：00：00）并且history_join_date有一些日期时，表示玩家加入了俱乐部（在该日期））。

现在，我有以下问题：

SELECT 
    player_id,
    player_nickname,
    team_id,
    team_name,
    history_join_date,
    history_end_date
FROM 
    players
        INNER JOIN history
            ON history.history_user_id = players.player_id
        INNER JOIN teams
            ON history.history_team_id = teams.team_id
ORDER BY 
    history_end_date DESC, 
    history_join_date DESC
LIMIT 7

但是，此查询返回类似的内容（使用上面的PHP过滤）：

(22-Aug-2012 23:05): Folha has left Portuguese Haxball Team.
(22-Aug-2012 00:25): mancini has left United.
(21-Aug-2012 01:29): PatoDaOldSchool has left Reign In Power.
(22-Aug-2012 23:37): Master has joined Born To Win.
(22-Aug-2012 23:28): AceR has joined Born To Win.
(22-Aug-2012 23:08): Nasri has joined Porto Club of Haxball.
(22-Aug-2012 18:53): Lloyd Banks has joined ARRIBA.

PHP过滤器：

foreach ($transfers as $transfer) {

//has joined
if($transfer['history_end_date']<$transfer['history_join_date']) {
    $type = ' has joined ';
    $date = date("d-M-Y H:i", strtotime($transfer['history_join_date']));
} else {
    $type = ' has left ';
    $date = date("d-M-Y H:i", strtotime($transfer['history_end_date']));
}

如您所见，在转移订单中，严格遵守日期（22-Aug =＆gt; 21-Aug =＆gt; 8-Aug）。

我在SQL中缺少什么？

问候！

Answer 1

问题是您是根据两个不同的值进行排序。所以你的结果首先由history_end_date排序，当结束日期相等时（即当它是默认值时），然后按history_join_date

排序。

（请注意，您的第一个结果都是结束，然后您的后续结果都是连接，并且每个子集都已正确排序）。

您对此数据结构有多少控制权？您可能能够重构历史表，以便只有一个日期，以及JOINED或END的历史记录类型......您可以查看joined_date和end_date并对其进行排序......

根据你在问题中的内容，我编写了以下DDL＆amp;数据：

create table players (
    player_id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, 
    player_nickname VARCHAR(255) NOT NULL UNIQUE
);

create table teams (
    team_id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
    team_name VARCHAR(255) NOT NULL UNIQUE
);

create table history (
    history_id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, 
    history_user_id INT NOT NULL, history_team_id INT NOT NULL, 
    history_join_date DATETIME NOT NULL, 
    history_end_date DATETIME NOT NULL DEFAULT "0000-00-00 00:00:00"
);

insert into players VALUES 
    (1,'Folha'),
    (2,'mancini'),
    (3,'PatoDaOldSchool'),
    (4,'Master'),
    (5,'AceR'),
    (6,'Nasri'),
    (7,'Lloyd Banks');

insert into teams VALUES 
    (1,'Portuguese Haxball Team'),
    (2,'United'),
    (3,'Reign In Power'),
    (4,'Born To Win'),
    (5,'Porto Club of Haxball'),
    (6,'ARRIBA');

insert into history VALUES 
    (DEFAULT,1,1,'2012-08-01 00:04','2012-08-22 23:05'),
    (DEFAULT,2,2,'2012-08-21 19:04','2012-08-22 00:25'),
    (DEFAULT,3,3,'2012-08-19 01:29','2012-08-21 01:29'),
    (DEFAULT,4,4,'2012-08-22 23:37',DEFAULT),
    (DEFAULT,5,4,'2012-08-22 23:28',DEFAULT),
    (DEFAULT,6,5,'2012-08-22 23:08',DEFAULT),
    (DEFAULT,7,6,'2012-08-22 18:53',DEFAULT);

解决方案一 - 历史事件视图

这显然不是唯一的解决方案（您必须根据需要评估选项，但您可以在MySQL中为您的历史事件创建一个视图并加入其中并使用它来进行类似以下的排序：

create view historyevent (
    event_user_id,
    event_team_id,
    event_date,
    event_type
) AS
    SELECT 
        history_user_id,
        history_team_id,
        history_join_date,
        'JOIN' 
    FROM history
    UNION
    SELECT
        history_user_id,
        history_team_id,
        history_end_date,
        'END'
    FROM history 
    WHERE history_end_date <> "0000-00-00 00:00:00";

然后你的选择变为：

SELECT 
    player_id,
    player_nickname,
    team_id,
    team_name,
    event_date,
    event_type
FROM players
INNER JOIN historyevent
        ON historyevent.event_user_id = players.player_id
INNER JOIN teams
        ON historyevent.event_team_id = teams.team_id
ORDER BY 
    event_date DESC;

这里的好处是你可以为同一个玩家获得连接和离开。

解决方案二 - 伪列。使用IF结构选择一列或另一列。

SELECT 
    player_id,
    player_nickname,
    team_id,
    team_name,
    history_join_date,
    history_end_date,
    IF(history_end_date>history_join_date,history_end_date,history_join_date) as order_date
FROM 
    players
    INNER JOIN history
        ON history.history_user_id = players.player_id
    INNER JOIN teams
        ON history.history_team_id = teams.team_id
ORDER BY 
    order_date DESC;

根据@ Barmar的回答，你也可以使用GREATEST()来挑选最好的参数。（MAX()是一个分组功能......实际上并不是你要找的东西）

Answer 2

我认为你想要的是：

ORDER BY MAX(history_join_date, history_end_date)

如何订购这种特定的内部连接？

2 个答案: