高效地将列转换为行

Question

你能帮我这个项目吗？ 我确实研究了先前提出的问题，但是它们似乎无法解决这种独特的情况。

样本数据：

 Member |    DOS    |  Dx1   |  Dx2  |  Dx3  | Dx4  | Dx5
 12345  | 1/1/2011  | 12142  | 12345 | 65657 | 5657 | 568
 56484  | 3/5/2011  | 568    | 56785 | 5695  | 575  | 168
 56872  | 2/12/2011 | 567    | 567   |

我需要看的是：

 Member DOS DX Seq
 12345 1/1/2011 12142 Dx1
 12345 1/1/2011 12345 Dx2
 12345 1/1/2011 65657 Dx3

等等。 仅显示那些Dx不为空-因此对于56872，我们只会看到Dx1和Dx2，而对于其他2，我们将看到所有5个Dx的记录。

有人可以帮助我吗？ 谢谢。

Answer 1

这种数据转换称为UNPIVOT 。 不幸的是，MySQL没有取消旋转功能，但是您可以通过几种不同的方式复制该功能。

您可以使用UNION ALL查询将每个列值转换为行：

select member, dos, dx, seq
from
(
  select member, dos, dx1 as dx, 'Dx1' as seq
  from yourtable
  union all
  select member, dos, dx2 as dx, 'Dx2' as seq
  from yourtable
  union all
  select member, dos, dx3 as dx, 'Dx3' as seq
  from yourtable
  union all
  select member, dos, dx4 as dx, 'Dx4' as seq
  from yourtable
  union all
  select member, dos, dx5 as dx, 'Dx5' as seq
  from yourtable
) d
where dx is not null
order by member, seq;

请参阅带有演示的SQL Fiddle 。 此方法将为您提供结果，但在较大的表上可能效率不高。

另一种方法是在虚拟表上使用CROSS JOIN：

select member, dos, dx, seq
from
(
  select t.member, t.dos, 
    case s.seq
      when 'Dx1' then dx1
      when 'Dx2' then dx2
      when 'Dx3' then dx3
      when 'Dx4' then dx4
      when 'Dx5' then dx5
    end DX,
    s.seq
  from yourtable t
  cross join
  (
    select 'Dx1' as seq union all
    select 'Dx2' as seq union all
    select 'Dx3' as seq union all
    select 'Dx4' as seq union all
    select 'Dx5' as seq
  ) s
) d
where dx is not null
order by member, seq;

请参阅带有演示的SQL Fiddle 。 两者都给出结果：

| MEMBER |                             DOS |    DX | SEQ |
|--------|---------------------------------|-------|-----|
|  12345 |  January, 01 2011 00:00:00+0000 | 12142 | Dx1 |
|  12345 |  January, 01 2011 00:00:00+0000 | 12345 | Dx2 |
|  12345 |  January, 01 2011 00:00:00+0000 | 65657 | Dx3 |
|  12345 |  January, 01 2011 00:00:00+0000 |  5657 | Dx4 |
|  12345 |  January, 01 2011 00:00:00+0000 |   568 | Dx5 |