mysql Select 来自多个不同列的值到单个列（PIVOT）

Question

+---------+------+--------+------+
|   year   | id  | band  | score | 
+---------+------+--------+------+
|    1990  |  1  | a     |  10  |
|    1991  | 1   | b     |  20  |
|    1992  | 1   | c     |  30  |
|    1993  | 1   | d     |  40  |
|    1994  | 1   | e     |  40  |
+---------+------+--------+------+

我想要如下所示的 output

+-------+-------+-------+-------+------+-----
| id    | 1990  | 1991  | 1992  |1993  | 1994 |
+-------+-------+-------+-------+------+------
|  1    |  10(a) | 20(b) | 30(c)| 40(d)| 50(e)|
-----------------------------------------------

Answer 1

您可以按如下方式进行声明：

SET @sql = NULL;
SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'max(case when year = ''',
      year,
      ''' then concat(score,''','(''',',band,',''')',''') end) year_',
      year
    )
  ) INTO @sql
FROM
  mytable;

SET @sql = CONCAT('SELECT id, ', @sql, ' 
                  FROM mytable 
                   GROUP BY id');
select @sql;


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

这是工作小提琴

Answer 2

使用条件聚合。 我认为将乐队和分数放在单独的列中更有意义，因此：

select id,
    max(case when year = 1990 then score end) score_1990,
    max(case when year = 1990 then band  end) band_1990,
    max(case when year = 1991 then score end) score_1991,
    max(case when year = 1991 then band  end) band_1991,
    ...
from mytable
group by id