MySQL的 - 錯誤＃1055連接表

Question

時，我有以下表格：

1. 遊戲：

   +----+-----------------------------------+ 
   | id | title        | 
   +----+-----------------------------------+ 
   | 1 | The Witcher      | 
   | 2 | The Witcher 2: Assassins of Kings | 
   | 3 | The Witcher 3: Wild Hunt   | 
   +----+-----------------------------------+ 
   

2. 平臺：

   +----+------+ 
   | id | name | 
   +----+------+ 
   | 1 | PC | 
   | 2 | MAC | 
   | 3 | X360 | 
   | 4 | PS3 | 
   | 5 | XONE | 
   | 6 | PS4 | 
   +----+------+ 
   

3. game_platform

   +----+---------+-------------+ 
   | id | id_game | id_platform | 
   +----+---------+-------------+ 
   | 1 |  1 |   1 | 
   | 2 |  1 |   2 | 
   | 3 |  2 |   1 | 
   | 4 |  2 |   2 | 
   | 5 |  2 |   3 | 
   | 6 |  3 |   1 | 
   | 7 |  3 |   5 | 
   | 8 |  3 |   6 | 
   +----+---------+-------------+ 
   

而作爲一個結果，我想是這樣的：

+-----------------------------------+----+-----+------+-----+------+-----+ 
    | game        | PC | MAC | X360 | PS3 | XONE | PS4 | 
    +-----------------------------------+----+-----+------+-----+------+-----+ 
    | The Witcher 3: Wild Hunt   | x |  |  |  | x | x | 
    +-----------------------------------+----+-----+------+-----+------+-----+ 

我使用的查詢是：

SELECT g.title as 'Title', 
IF (gp.id_platform = 1, 'x', '') as 'PC', 
IF (gp.id_platform = 2, 'x', '') as 'MAC', 
IF (gp.id_platform = 3, 'x', '') as 'X360', 
IF (gp.id_platform = 4, 'x', '') as 'PS3' 
IF (gp.id_platform = 5, 'x', '') as 'XONE' 
IF (gp.id_platform = 6, 'x', '') as 'PS4' 
FROM game g LEFT JOIN (platform pl, game_platform gp) ON (g.id = gp.id_game and pl.id = gp.id_platform) 
WHERE g.id = 1; 

，一切都很好，除了數據呈現這樣的：

+-----------------------------------+----+-----+------+-----+------+-----+ 
    | game        | PC | MAC | X360 | PS3 | XONE | PS4 | 
    +-----------------------------------+----+-----+------+-----+------+-----+ 
    | The Witcher 3: Wild Hunt   | x |  |  |  |  |  | 
    | The Witcher 3: Wild Hunt   | |  |  |  | x |  | 
    | The Witcher 3: Wild Hunt   | |  |  |  |  | x | 
    +-----------------------------------+----+-----+------+-----+------+-----+ 

當我在末尾添加GROUP BY子句：

SELECT g.title as 'Title', 
IF (gp.id_platform = 1, 'x', '') as 'PC', 
IF (gp.id_platform = 2, 'x', '') as 'MAC', 
IF (gp.id_platform = 3, 'x', '') as 'X360', 
IF (gp.id_platform = 4, 'x', '') as 'PS3' 
IF (gp.id_platform = 5, 'x', '') as 'XONE' 
IF (gp.id_platform = 6, 'x', '') as 'PS4' 
FROM game g INNER JOIN (platform pl, game_platform gp) ON (g.id = gp.id_game and pl.id = gp.id_platform) 
WHERE g.id = 1 
GROUP BY g.title; 

我收到提示：

#1055 - Expression #2 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'db_klimos.gp.id_platform' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by 

如果我的gp.id_platform添加到GROUP BY條款，我得到的初步結果，如果數據沒有進行分組。

是否有一種方法來分組表中的數據，因爲我想不更改sql_mode = only_full_group_by？ 我已經知道這個選項的含義以及它爲什麼被引入。我使用的數據庫不是自己託管的數據庫，因此無論如何我都無法將其關閉。

Answer 1

使用CASE代替IF並選擇MAX值，從而獲得所需結果

試試這個

SELECT g.title as 'Title', 
MAX(CASE WHEN gp.id_platform = 1 then 'x' ELSE '' END) as 'PC', 
MAX(CASE WHEN gp.id_platform = 2 then 'x' ELSE '' END) as 'MAC', 
MAX(CASE WHEN gp.id_platform = 3 then 'x' ELSE '' END) as 'X360', 
MAX(CASE WHEN gp.id_platform = 4 then 'x' ELSE '' END) as 'PS3', 
MAX(CASE WHEN gp.id_platform = 5 then 'x' ELSE '' END) as 'XONE', 
MAX(CASE WHEN gp.id_platform = 6 then 'x' ELSE '' END) as 'PS4' 
FROM game g LEFT JOIN (platform pl, game_platform gp) ON (g.id = gp.id_game and pl.id = gp.id_platform) 
WHERE g.id = 1