MySQL动态数据透视表

Question

我试图让动态列的数据透视表工作。当user_id是一个字符串，它工作正常，但如果它的一个int，那么似乎失败

这里是我迄今为止与过去问题的援助：

CREATE TABLE measure2 
    (`inspection_date` date, `user_id` int, `score` int, comment text) 
; 

INSERT INTO measure2 
    (`inspection_date`, `user_id`, `score`, comment) 
VALUES 
    ('2012-10-16', 0, 0, null), 
    ('2012-10-16', 1, 0, null), 
    ('2012-10-16', 2, 0, null), 
    ('2012-10-16', 3, 0, null), 
    ('2012-10-17', 0, 1, null), 
    ('2012-10-17', 1, 1, null), 
    ('2012-10-17', 2, 1, null), 
    ('2012-10-18', 3, 1, null) 
; 


SET @sql = NULL; 
SELECT 
    GROUP_CONCAT(DISTINCT 
    CONCAT(
     'max(case when user_id = ''', 
     user_id, 
     ''' then score end) AS ', 
     user_id 
    ) 
) INTO @sql 
FROM measure2; 

SET @sql = CONCAT('SELECT inspection_date, ', @sql, ' 
        FROM measure2 
        GROUP BY inspection_date'); 

PREPARE stmt FROM @sql; 
EXECUTE stmt; 
DEALLOCATE PREPARE stmt; 

见：http://sqlfiddle.com/#!2/eab24/1

林肯定它的东西很简单，但我错过了什么？

感谢

Answer 1

由于值在int你正在使他们的列名，你必须包装在反引号的值

的SQL的样子：

max(case when user_id = 1 then score end) as `1` 

完整的查询将是：

SET @sql = NULL; 
SELECT 
    GROUP_CONCAT(DISTINCT 
    CONCAT(
     'max(case when user_id = ''', 
     user_id, 
     ''' then score end) AS `', 
     user_id, '`' 
    ) 
) INTO @sql 
FROM measure2; 

SET @sql = CONCAT('SELECT inspection_date, ', @sql, ' 
        FROM measure2 
        GROUP BY inspection_date'); 

PREPARE stmt FROM @sql; 
EXECUTE stmt; 
DEALLOCATE PREPARE stmt; 

请参阅SQL Fiddle with Demo

Answer 2

确实简单 - 单独号码不是有效的SQL列名，因此你需要修改你的代码它们放在反引号：

SET @sql = NULL; 
SELECT 
    GROUP_CONCAT(DISTINCT 
    CONCAT(
     'max(case when user_id = ', 
     user_id, 
     ' then score end) AS `', 
     user_id, 
     '`' 
    ) 
) INTO @sql 
FROM measure2; 

SET @sql = CONCAT('SELECT inspection_date, ', @sql, ' 
        FROM measure2 
        GROUP BY inspection_date'); 

PREPARE stmt FROM @sql; 
EXECUTE stmt; 
DEALLOCATE PREPARE stmt; 

我建议保留这一变化为字符串值，以及，以防某些字符串值与保留字匹配或包含空格。

（另外，'不需要围绕数字值，所以我从壳体移除子句它们。）

SQLFiddle here。