MySQL的數據透視表

Question

我想編寫一個查詢來創建數據的「表」如下：

SELECT cs.`category_id`, cs.`ProcessDate`, cs.`PercentChange` 
    FROM `Category_Statistics` cs 
WHERE cs.`ProcessDate` >= '2011-05-10' 
    AND cs.`ProcessDate` <= '2011-05-14' 

這將返回類似：

CategoryId | ProcessDate | PercentChange 
------------------------------------------- 
category_4 | 2011-05-10 |  10 
category_4 | 2011-05-11 |  18 
category_4 | 2011-05012 |  12 
... 
category_7 | 2011-05-10 |  21 
category_7 | 2011-05-11 |  7 
... 
category_12 | 2011-05-10 |  7 
category_12 | 2011-05-11 |  15 

現在我希望結果是這樣的（從MySQL查詢，而不是由應用程序操作）：

CategoryId | 2011-05-10 | 2011-05-11 | 2011-05-12 | 2011-05-13 | 2011-05-14 | 
-------------------------------------------------------------------------------- 
category_4 |  10  |  18  |  12  |  9  |  14 | 
category_7 |  21  |  7  |  16  |  14 |  13 | 
categeory_12 |  7  |  15  |  11  |  19 |  8 | 
-------------------------------------------------------------------------------- 

有兩個警告這樣：

1. 日期範圍可以擴大或縮小 （取決於查詢）

2. PercentChange可能在某些情況下， 空（可以說category_7/ 2011-05-12可能沒有設置值）

所以，最後我不太清楚如何構建查詢的選擇部分，以反映列的動態數（我知道它是與CONCAT）。

編輯 - >部分的工作代碼 - >

SELECT `CategoryId`, 
    MAX(IF(c.`ProcessedOn` = '2011-04-20', c.`PercentChange`, NULL)) AS '2011-04-20', 
    MAX(IF(c.`ProcessedOn` = '2011-04-21', c.`PercentChange`, NULL)) AS '2011-04-21', 
    MAX(IF(c.`ProcessedOn` = '2011-04-22', c.`PercentChange`, NULL)) AS '2011-04-22', 
    MAX(IF(c.`ProcessedOn` = '2011-04-23', c.`PercentChange`, NULL)) AS '2011-04-23', 
    MAX(IF(c.`ProcessedOn` = '2011-04-24', c.`PercentChange`, NULL)) AS '2011-04-24' 
    FROM `Category_Gravity` c 
WHERE c.`ProcessedOn` >= '2011-04-20' 
    AND c.`ProcessedOn` <= '2011-04-24' 
GROUP BY `CategoryId` 

我現在需要做的是打開

MAX(IF(c.`ProcessedOn` = '2011-04-20', c.`PercentChange`, NULL)) AS '2011-04-20', 

到的東西更多動態的（因爲我的日期範圍將發生變化）

Answer 1

看看這個類似的線程，我寫了一個sp來完成任務

Join two tables (with a 1-M relationship) where the second table needs to be 'flattened' into one row

編輯。更新答案

create table `pivot` (
    `id` int(11) not null auto_increment, 
    `categoryid` int(11) default null, 
    `processdate` date default null, 
    `percentchange` int(11) default null, 
    primary key (`id`) 
) engine=myisam auto_increment=9 default charset=latin1; 

/*Data for the table `pivot` */ 

insert into `pivot`(`id`,`categoryid`,`processdate`,`percentchange`) values (1,4,'2011-05-10',1); 
insert into `pivot`(`id`,`categoryid`,`processdate`,`percentchange`) values (2,4,'2011-05-11',22); 
insert into `pivot`(`id`,`categoryid`,`processdate`,`percentchange`) values (3,4,'2011-05-12',3); 
insert into `pivot`(`id`,`categoryid`,`processdate`,`percentchange`) values (4,7,'2011-05-10',4); 
insert into `pivot`(`id`,`categoryid`,`processdate`,`percentchange`) values (5,7,'2011-05-11',5); 
insert into `pivot`(`id`,`categoryid`,`processdate`,`percentchange`) values (6,12,'2011-05-10',6); 
insert into `pivot`(`id`,`categoryid`,`processdate`,`percentchange`) values (7,12,'2011-05-12',7); 
insert into `pivot`(`id`,`categoryid`,`processdate`,`percentchange`) values (8,4,'2011-05-13',12); 



delimiter // 
drop procedure if exists dynamic_view2// 
create procedure dynamic_view2(in sdate date,in edate date) 
begin 
declare finish int default 0; 
declare cdate date; 
declare str varchar(10000) default "select categoryid,"; 
declare curs cursor for select processdate from pivot where processdate between sdate and edate group by processdate; 
declare continue handler for not found set finish = 1; 
open curs; 
my_loop:loop 
fetch curs into cdate; 
if finish = 1 then 
leave my_loop; 
end if; 
set str = concat(str, "max(case when processdate = '",cdate,"' then percentchange else null end) as `",cdate,"`,"); 
end loop; 
close curs; 
set str = substr(str,1,char_length(str)-1); 
set @str = concat(str," from pivot 
      group by categoryid"); 

prepare stmt from @str; 
execute stmt; 
deallocate prepare stmt; 
end;// 
delimiter ; 


mysql> call dynamic_view2('2011-05-10','2011-05-13'); 
+------------+------------+------------+------------+------------+ 
| categoryid | 2011-05-10 | 2011-05-11 | 2011-05-12 | 2011-05-13 | 
+------------+------------+------------+------------+------------+ 
|   4 |   1 |   22 |   3 |   12 | 
|   7 |   4 |   5 |  NULL |  NULL | 
|   12 |   6 |  NULL |   7 |  NULL | 
+------------+------------+------------+------------+------------+ 
3 rows in set (0.00 sec)