mysql将2列移至一列，而不是0的数据

Question

可以将此表重新安排到一个表中（使用视图）

+----+------+--------+
| id | item1| item2  |
+----+------+--------+
|  1 |    A |  B     |
|  2 |    0 |  B     |
|  3 |    A |  0     |
|  4 |    0 |  0     |
+----+------+--------+

将数据移动到这种安排：

+----+------+
| id |items |
+----+------+
|  1 |    A |
|  2 |    B |
|  3 |    B |
|  4 |    A |
+----+------+

Answer 1

我认为在忽略0值的同时取消数据透视。

考虑：

select 
    row_number() over(order by id, seq) id,
    item
from (
    select id, 1 seq, item1 item from mytable where item1 <> 0
    union all select id, 2, item2 from mytable where item2 <> 0
) t
order by id, seq