Mysql将列转换为行（数据透视表）

Question

我有一张这样的桌子

+---+-----+----+----+----+----+
|id |month|col1|col2|col3|col4|
+---+-----+----+----+----+----+
|101|Jan  |A   |B   |NULL|B   |
+---+-----+----+----+----+----+
|102|feb  |C   |A   |G   |E   |
+---+-----+----+----+----+----+

然后我想创建这样的报告

+----+---+---+
|desc|jan|feb|
+----+---+---+
|col1|A  |C  |
+----+---+---+
|col2|B  |A  |
+----+---+---+
|col3|0  |G  |
+----+---+---+
|Col4|B  |E  |
+----+---+---+

有人可以帮忙吗？

Answer 1

您需要首先对数据进行反透视，然后对其进行透视。但不幸的是，MySQL 没有这些函数，因此您需要使用 UNION ALL 查询 unpivot 和聚合函数以及 CASE 来复制它们。

unpivot 或UNION ALL 部分从您的 col1、col2 等获取数据并将其转换为多行：

select id, month, col1 value, 'col1' descrip
from yourtable
union all
select id, month, col2 value, 'col2' descrip
from yourtable
union all
select id, month, col3 value, 'col3' descrip
from yourtable
union all
select id, month, col4 value, 'col4' descrip
from yourtable

见SQL Fiddle with Demo。

结果：

|  ID | MONTH |  VALUE | DESCRIP |
----------------------------------
| 101 |   Jan |      A |    col1 |
| 102 |   feb |      C |    col1 |
| 101 |   Jan |      B |    col2 |
| 102 |   feb |      A |    col2 |
| 101 |   Jan | (null) |    col3 |
| 102 |   feb |      G |    col3 |
| 101 |   Jan |      B |    col4 |
| 102 |   feb |      E |    col4 |

然后您将其包装在子查询中以应用聚合和 CASE 以将其转换为您想要的格式：

select descrip, 
  max(case when month = 'jan' then value else 0 end) jan,
  max(case when month = 'feb' then value else 0 end) feb
from
(
  select id, month, col1 value, 'col1' descrip
  from yourtable
  union all
  select id, month, col2 value, 'col2' descrip
  from yourtable
  union all
  select id, month, col3 value, 'col3' descrip
  from yourtable
  union all
  select id, month, col4 value, 'col4' descrip
  from yourtable
) src
group by descrip

见SQL Fiddle with demo

结果是：

| DESCRIP | JAN | FEB |
-----------------------
|    col1 |   A |   C |
|    col2 |   B |   A |
|    col3 |   0 |   G |
|    col4 |   B |   E |

Answer 2

虽然这个问题太老了，有人将其标记为“非常常见”，但人们似乎仍然发现它（包括我）并觉得它很有帮助。我开发了一个更通用的版本来取消旋转一行，并认为它可能对某人有所帮助。

SET @target_schema='schema';
SET @target_table='table';
SET @target_where='`id`=1';
SELECT
    GROUP_CONCAT(qry SEPARATOR ' UNION ALL ')
    INTO @sql
FROM (
    SELECT
        CONCAT('SELECT `id`,', QUOTE(COLUMN_NAME), ' AS `key`,`', COLUMN_NAME, '` AS `value` FROM `', @target_table, '` WHERE ', @target_where) qry
    FROM (
        SELECT `COLUMN_NAME` 
        FROM `INFORMATION_SCHEMA`.`COLUMNS` 
        WHERE `TABLE_SCHEMA`=@target_schema 
            AND `TABLE_NAME`=@target_table
    ) AS `A`
) AS `B`;
PREPARE s FROM @sql; EXECUTE s; DEALLOCATE PREPARE s;

我在 MySQL 8.x 服务器上使用此查询并将其聚合到那里的 JSON 对象，因此id, key, value 结果结构。