如何從多個mysql列中選擇不同的值並將它們放入一個PHP數組中？

Question

我有一張歌曲表格，每首歌曲最多可以有3種不同的風格。所以在我的表格中，對於每首歌曲，我都有列genre1，genre2和genre3。我正在嘗試顯示列表中可用的所有流派。

這裏是一個隨便舉個例子集：

genre1 genre2 genre3 
metal  jazz 
metal  country pop 
oldies metal 
rap 
jazz  hip-hop choir 
choir  metal  jazz 

我想要的清單，在PHP完成的，按字母順序顯示可用的不同類型可供選擇。因此，它應該列出此：

• 合唱
• 國家
• 街舞
• 爵士
• 金屬
• 老歌
• 流行
• 說唱

所有幫助表示讚賞。也許我不會以最聰明的方式去做這件事，但我想不出更好的辦法。

Answer 1

所以單獨列不有所作爲？如果是這樣的話，你可以使用一個UNION

SELECT genre1 AS g FROM t UNION SELECT genre2 AS g FROM t UNION SELECT genre3 AS g FROM t 

如果你有一個WHERE條款，那麼你將需要複製的3倍，或使用中間臨時表

祝你好運！

---

表：

mysql> SELECT genre1, genre2, genre3 FROM music; 
+--------+---------+--------+ 
| genre1 | genre2 | genre3 | 
+--------+---------+--------+ 
| metal | jazz |  | 
| metal | country | pop | 
| oldies | metal |  | 
| rap |   |  | 
| jazz | hip-hop | choir | 
| choir | metal | jazz | 
+--------+---------+--------+ 
6 rows in set (0.00 sec) 

分組：

mysql> SELECT genre1 AS g FROM music UNION ALL 
      SELECT genre2 AS g FROM music UNION ALL 
      SELECT genre3 AS g FROM music 
+---------+ 
| g  | 
+---------+ 
| metal | 
| metal | 
| oldies | 
| rap  | 
| jazz | 
| choir | 
| jazz | 
| country | 
| metal | 
|   | 
| hip-hop | 
| metal | 
|   | 
| pop  | 
|   | 
|   | 
| choir | 
| jazz | 
+---------+ 
18 rows in set (0.00 sec) 

計數：

mysql> SELECT g, COUNT(*) AS c FROM 
      (SELECT genre1 AS g FROM music UNION ALL 
       SELECT genre2 AS g FROM music UNION ALL 
       SELECT genre3 AS g FROM music) 
     AS tg GROUP BY g; 
+---------+---+ 
| g  | c | 
+---------+---+ 
|   | 4 | 
| choir | 2 | 
| country | 1 | 
| hip-hop | 1 | 
| jazz | 3 | 
| metal | 4 | 
| oldies | 1 | 
| pop  | 1 | 
| rap  | 1 | 
+---------+---+ 
9 rows in set (0.01 sec) 

Answer 2

SELECT DISTINCT genre1，genre2，genre3 FROM TABEL

Description

也許你需要更好的數據庫設計... songs | genres | [song_id|genre_id]

Answer 3

SELECT genre1, genre2, genre3 FROM table 

假設該共mes作爲數組陣列，然後：

function coalesce_into_array($aggregate, $row) { 
    foreach ($row as $genre) { 
     $aggregate[] = $genre; 
    } 

    return $aggregate; 
} 

$data = array_unique(array_reduce($data, 'coalesce_into_array', array())); 
sort($data); 

但是，我不會在一個嚴重的應用程序中推薦這個。數據庫設計不好。閱讀有關數據庫規範化的信息，瞭解如何改進它。

Answer 4

除非你denormalized（2）流派到三列出於性能的考慮，應該有相關的歌曲和流派一個單獨的表：

CREATE TABLE SongGenres (
    song INT NOT NULL REFERENCES Songs (id) ON DELETE CASCADE, 
    genre VARCHAR(32) NOT NULL, 
    UNIQUE INDEX (song, genre), 
    INDEX genres (genre) -- improves performance for getting genre names 
) Engine=InnoDB; 

這摒棄了要求的（「十字街藍調「可以在」藍調「和」三角洲藍調「下提交，但這就是關於它）和人工限制（A3的鄉村酸屋福音浮現在腦海中）每首歌的三種流派。如果您有一套有限的流派，您可能需要製作流派專欄enumerated。該SongGenres表進行了簡化讓所有流派：

SELECT UNIQUE genre FROM SongGenres; 

另外，還可以進一步規範和創造流派單獨的表：

CREATE TABLE Genres (
    id INT PRIMARY KEY AUTO_INCREMENT, 
    name VARCHAR(32) NOT NULL, 
    UNIQUE INDEX (name) 
) Engine=InnoDB; 

CREATE TABLE SongGenres (
    song INT NOT NULL REFERENCES Songs (id) ON DELETE CASCADE, 
    genre INT NOT NULL REFERENCES Genres (id) ON DELETE RESTRICT, 
    UNIQUE INDEX (song, genre) 
) Engine=InnoDB; 

簡化了獲取所有種類名甚至更多（儘管這只是一個第二個優點）：

SELECT name FROM Genres; 

到流派表的主要優點是數據正確性：如果有人拼錯流派，它不會被在流派發現噸能夠。一個潛在的缺點是它將有效的流派限制在表格中的那些流派。當然，給予SongGenres上擁有INSERT權限的用戶帳號是有意義的，所以這個限制並不嚴重。一旦你開始添加新的流派，你將面臨與沒有流派表的錯誤相同的問題：打字錯誤。而不是添加流派表中找不到的新流派，查找類似的流派（例如，使用Levenshtein distance或SOUNDS LIKE），如果找到任何流派，請詢問用戶是否要用發現的流派或保留原始類型（並將其添加到流派列表中）。

這裏的數據是什麼樣子在第一種情況下（兩個表，Songs和SongGenres）：

mysql> SELECT * FROM Songs; 
+----+---------------------+--------+---- 
| id | title    | artist | ... 
+----+---------------------+--------+---- 
| 1 | Cross Road Blues | ... 
| 2 | Peace In the Valley | ... 
+----+---------------------+--------+---- 
2 rows in set (0.00 sec) 

mysql> SELECT * FROM SongGenres; 
+------+-------------+ 
| song | genre  | 
+------+-------------+ 
| 2 | acid  | 
| 1 | blues  | 
| 2 | country  | 
| 1 | delta blues | 
| 2 | gospel  | 
| 2 | house  | 
| 2 | techno  | 
+------+-------------+ 
7 rows in set (0.00 sec) 

mysql> SELECT s.title, sg.genre FROM Songs AS s JOIN SongGenres AS sg ON s.id=sg.song; 
+---------------------+-------------+ 
| title    | genre  | 
+---------------------+-------------+ 
| Cross Road Blues | blues  | 
| Cross Road Blues | delta blues | 
| Peace In the Valley | acid  | 
| Peace In the Valley | country  | 
| Peace In the Valley | gospel  | 
| Peace In the Valley | house  | 
| Peace In the Valley | techno  | 
+---------------------+-------------+ 
7 rows in set (0.00 sec) 

設有一個獨立的流派表，在歌曲中的數據會看起來一樣，但在其他我們會有類似的表格：

mysql> SELECT * FROM Genres; 
+----+-------------+ 
| id | name  | 
+----+-------------+ 
| 1 | acid  | 
| 2 | blues  | 
| 3 | classical | 
| 4 | country  | 
| 5 | delta blues | 
| 6 | folk  | 
| 7 | gospel  | 
| 8 | hip-hop  | 
| 9 | house  | 
... 
| 18 | techno  | 
+----+-------------+ 
18 rows in set (0.00 sec) 

mysql> SELECT * FROM SongGenres; 
+------+-------+ 
| song | genre | 
+------+-------+ 
| 1 |  2 | 
| 1 |  5 | 
| 2 |  1 | 
| 2 |  4 | 
| 2 |  7 | 
| 2 |  9 | 
| 2 | 18 | 
+------+-------+ 
7 rows in set (0.00 sec) 

mysql> SELECT s.title, g.name AS genre 
    -> FROM Songs AS s 
    ->  JOIN SongGenres AS sg ON s.id=sg.song 
    ->  JOIN Genres AS g ON sg.genre=g.id; 
+---------------------+-------------+ 
| title    | genre  | 
+---------------------+-------------+ 
| Cross Road Blues | blues  | 
| Cross Road Blues | delta blues | 
| Peace In the Valley | acid  | 
| Peace In the Valley | country  | 
| Peace In the Valley | gospel  | 
| Peace In the Valley | house  | 
| Peace In the Valley | techno  | 
+---------------------+-------------+ 
7 rows in set (0.00 sec)