如何從mysql數據庫表中檢索最後10條記錄？

Question

我有一個奇怪的問題。當我運行這個腳本時，我從數據庫中獲得了10條記錄，但它們都完全一樣。我不知道我在做什麼錯誤或如何解決它。請幫幫我。

我有表AMCMS_highscores，AMCMS_users，AMCMS_games我想看看AMCMS_highscores表內，得到最後10條記錄，但只有場gameid是1997年例如。任何幫助表示讚賞。

$data = query("SELECT `AMCMS_highscores`.`primkey` , `AMCMS_highscores`.`gameid` , `AMCMS_highscores`.`score` , `AMCMS_users`.`username` , `AMCMS_highscores`.`status` , `AMCMS_highscores`.`userkey` , `AMCMS_games`.`primkey` , `AMCMS_games`.`gamename` FROM `AMCMS_highscores` , `AMCMS_games` , `AMCMS_users` WHERE `AMCMS_highscores`.`gameid` = '$gameid' AND `AMCMS_highscores`.`userkey` != `AMCMS_users`.`userkey` AND `AMCMS_highscores`.`gameid` = `AMCMS_games`.`primkey` AND `AMCMS_highscores`.`status`= 'approved' ORDER by `AMCMS_highscores`.`primkey` DESC LIMIT 0, 10"); 

Print "<table border cellpadding=3>"; 
while($info = mysql_fetch_array($data)) { 
    Print "<tr>"; 
    Print "<th>Score:</th> <td>".$info['score'] . "</td> "; 
    Print "<th>ID:</th> <td>".$info['userkey'] . " </td></tr>"; } 
Print "</table>"; 

下面是查詢的格式化版本：

SELECT 
    `AMCMS_highscores`.`primkey` , `AMCMS_highscores`.`gameid` , 
    `AMCMS_highscores`.`score` , `AMCMS_users`.`username` , 
    `AMCMS_highscores`.`status` , `AMCMS_highscores`.`userkey` , 
    `AMCMS_games`.`primkey` , `AMCMS_games`.`gamename` 
FROM `AMCMS_highscores` , `AMCMS_games` , `AMCMS_users` 
WHERE `AMCMS_highscores`.`gameid` = '$gameid' 
AND `AMCMS_highscores`.`userkey` != `AMCMS_users`.`userkey` 
AND `AMCMS_highscores`.`gameid` = `AMCMS_games`.`primkey` 
AND `AMCMS_highscores`.`status`= 'approved' 
ORDER by `AMCMS_highscores`.`primkey` DESC 
LIMIT 0, 10 

---

哎呀，我沒有故意要複製，但我沒有意外。 當它與「=」號（highscores.userkey = users.userkey）我得到空的查詢，以便didnt解決它:(

我希望這個查詢是比較容易理解:)

SELECT highscores.primkey, highscores.gameid, highscores.score, users.username, 
highscores.status, highscores.userkey, games.primkey, games.gamename 

FROM AMCMS_highscores AS highscores, AMCMS_games as games, AMCMS_users as users 

WHERE highscores.gameid = '$gameid' AND 
     highscores.status = 'approved' 

ORDER by highscores.primkey DESC LIMIT 0, 10 

下面是結果：

http://www.gamesorbiter.com/FB_app/play.php?gameid=1997 （在遊戲中）

順便說一句，當你將它張貼你如何編寫查詢？我點擊了代碼按鈕，只有代碼的第一行被編碼。

Answer 1

如果您嘗試從AMCMS_users中選擇AMCMS_highscores中沒有匹配行的記錄，那麼您需要執行LEFT JOIN，並在連接表中測試NULL值。下面是JOIN Syntax的摘錄：

如果在一個LEFT JOIN沒有匹配一行在ON或USING 部分 右表，設置爲NULL所有 列一排用於 右表。

您的查詢會因此看起來更像是這樣的：：

SELECT 
    `AMCMS_highscores`.`primkey` , `AMCMS_highscores`.`gameid` , 
    `AMCMS_highscores`.`score` , `AMCMS_users`.`username` , 
    `AMCMS_highscores`.`status` , `AMCMS_highscores`.`userkey` , 
    `AMCMS_games`.`primkey` , `AMCMS_games`.`gamename` 
FROM `AMCMS_highscores` 
LEFT JOIN `AMCMS_users` 
    ON `AMCMS_highscores`.`userkey` = `AMCMS_users`.`userkey` 
JOIN `AMCMS_games` 
    ON `AMCMS_highscores`.`gameid` = `AMCMS_games`.`primkey` 
WHERE `AMCMS_highscores`.`gameid` = '$gameid' 
AND `AMCMS_highscores`.`status`= 'approved' 
AND `AMCMS_users`.`userkey` = NULL 
ORDER by `AMCMS_highscores`.`primkey` DESC 
LIMIT 0, 10; 

暫時忽略其他的條件可以在那些在另一個表中沒有 對應表中利用這一點來 查找行，您的查詢正在查看AMCMS_highscores中的每一行，並將其加入AMCMS_highscores中的每一行，其中AMCMS_highscores。 userkey不等於AMCMS_users。 userkey。這會產生很多匹配的行。要查看發生了什麼，請從查詢中刪除LIMIT子句。

Answer 2

與別名同樣的事情，一個更好的格式：

SELECT highscores.primkey, highscores.gameid, highscores.score, users.username, 
highscores.status, highscores.userkey, games.primkey, games.gamename 

FROM AMCMS_highscores AS highscores, AMCMS_games as games, AMCMS_users as users 

WHERE highscores.gameid = '$gameid' AND 
     highscores.userkey != users.userkey AND 
     highscores.gameid = games.primkey AND 
     highscores.status = 'approved' 

ORDER by highscores.primkey DESC LIMIT 0, 10 

你沒有說什麼表計劃是，但我的猜測是，這個問題是在WHERE部分，更具體highscores.userkey != users.userkey。它僅接受不具有與高分表中的用戶相同的用戶。嘗試將!=更改爲=。