MySQL动态数据透视表

Question

我试图获得一个带有动态列的数据透视表。当user_id是一个字符串时，它可以正常工作，但是如果它是一个int，那么它似乎会失败

到目前为止，在过去的问题帮助下，我得到的是：

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;

参见：http :
//sqlfiddle.com/#!2/eab24/1

我确定这很简单，但是我想念什么呢？

谢谢

Answer 1

由于值在int其中，因此您要将它们设为列名，因此必须将值包装在反引号中

该SQL将看起来像：

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;

参见带有演示的SQL Fiddle