MySQL - How to unpivot columns to rows?

Question

I\'m probably not seeing things very clear at this moment, but I have a table in MySQL which looks like this:

ID | a  | b  | c 
1  | a1 | b1 | c1
2  | a2 | b         


        

Answer 1

You are trying to unpivot the data. MySQL does not have an unpivot function, so you will have to use a UNION ALL query to convert the columns into rows:

select id, 'a' col, a value
from yourtable
union all
select id, 'b' col, b value
from yourtable
union all
select id, 'c' col, c value
from yourtable

See SQL Fiddle with Demo.

This can also be done using a CROSS JOIN:

select t.id,
  c.col,
  case c.col
    when 'a' then a
    when 'b' then b
    when 'c' then c
  end as data
from yourtable t
cross join
(
  select 'a' as col
  union all select 'b'
  union all select 'c'
) c

See SQL Fiddle with Demo