Question

我试图获得一个包含动态列的数据透视表。当user_id是一个字符串时，它工作正常，但如果它是一个int，那么它似乎失败

到目前为止，这是我在过去的问题的帮助下所得到的：

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;

请参阅：http://sqlfiddle.com/#!2/eab24/1

我确定它很简单，但我错过了什么？

由于

Answer 1

由于值在int中，你正在使它们成为列名，你必须将值包装在反引号中

sql看起来像：

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

完整查询将是：

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

确实很简单 - 数字本身并不是SQL中的有效列名，因此您需要修改代码以将其括在反引号中：

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;

我建议保留字符串值的更改，以防某些字符串值与保留字匹配或包含空格。

（另外，数字值周围不需要'，所以我已从case子句中删除它们。）

SQLFiddle here。

MySQL动态数据透视表

2 个答案: