求教sql
有个表tab
AA BB
1 a
2 b
3 c
4 d


查出结果是ab ac ad bc bd cd
[解决办法]
如果不考虑效率问题

with t1 as
(
select 1 c1,'a' c2 from dual
union all
select 2 c1,'b' c2 from dual
union all
select 3 c1,'c' c2 from dual
union all
select 4 c1,'d' c2 from dual
)

select a.c2
[解决办法]
b.c2 c1
from t1 a full join t1 b on a.c2 < b.c2
where length(a.c2
[解决办法]
b.c2) > length(a.c2)

c1
------------------
1ab
2ac
3ad
4bc
5bd
6cd