高效地将列转换为行

Question

Can you please help me with this project? I did research the prior asked questions, but they don't seem to address this unique situation.

Sample data:

 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   |

What I need to see is this:

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

and so forth. Only showing those Dx where not null- so for 56872, we'd only see Dx1 and Dx2, but for the other 2, we'd see records for all 5 Dx.

Is anyone able to help me? Thank you.

Answer 1

This type of data transformation is called an UNPIVOT . Unfortunately MySQL doesn't have an unpivot function but you can replicate the functionality a few different ways.

You can use a UNION ALL query to convert each column value into rows:

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;

See SQL Fiddle with Demo . This method will get you the result but it might not be very efficient on larger tables.

Another method would be using a CROSS JOIN on a virtual table:

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;

See SQL Fiddle with Demo . Both give a result:

| 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 |