MySQL – Wie konvertiere ich Spalten in Zeilen?

Question

ID |
1 |. a1 |. b1 |
2 |. a2 |. b2 |.
<p>Wie reorganisiere ich Zeilen in IDs, Spaltenüberschriften und Werte? </p>
<pre class="brush:php;toolbar:false;">1 |
1 |. b1 |
1|c1|c
2 |. a2 |
2 |. b2 |
2 |. c2 |. c

Answer 1

您正在尝试对数据进行反转。MySQL没有反转函数，因此您需要使用UNION ALL查询将列转换为行：

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.

这也可以使用CROSS JOIN来实现：

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