oralce 列拆分
id a1 a2 a3
-----------------------
01 r1 r2 r3
02 r1 r3
03 r1 r2

如何将上面的表拆分成下面的样子：

id a
--------------
01 r1
01 r2
01 r3
02 r1
02 r3
03 r1
03 r2





[解决办法]

select * from (
select id,  decode(lvl, 1, a1, 2, a2, 3, a3) as a              
from t, (select level lvl from dual connect by level <= 3)
) where a is not null order by id, a;