移調MySQL的鍵值表

Question

我有一個這樣的表：

+------+---------+-------------+------+ 
| id | key  | value  | user | 
+------+---------+-------------+------+ 
| 1 | first | foo   | 32 | 
| 2 | second | bar   | 32 | 
| 3 | system | more  | 32 | 
| 4 | first | galaxy  | 21 | 
| 5 | second | foo   | 45 | 
| 6 | system | other  | 45 | 
+------+---------+-------------+------+ 

，我需要變換成：

+-----------+------------+---------+------+ 
| first  | second  | system | user | 
+-----------+------------+---------+------+ 
| foo  | bar  | more | 32 | 
| galaxy | NULL  | NULL | 21 | 
| NULL | foo  | other | 45 | 
+-----------+------------+---------+------+ 

它不使用ID，關鍵列將在colums中進行轉換，結果將按用戶分組，並且不存在的值將被設置爲NULL。那可能嗎？

編輯：我忘了說鍵參數是動態的，事先不知道。

Answer 1

嘗試此查詢：

INSERT INTO transposed_table (first, second, system, user) 
SELECT t1.value, t2.value, t3.value, t1.user 
FROM initial_table as t1 
OUTER_JOIN initial_table as t2 ON t2.user = t1.user 
OUTER_JOIN initial_table as t3 ON t3.user = t2.user; 

當我打電話transposed_table新目標表，initial_table你已經有一個。