select查询问题

Question

SQL> select * from a;                           A1 A2
----------------------------- ----------
                            8 a
                            2 ba
                            3 ca
                            4 daSQL> select * from b;                           B1 B2
----------------------------- ----------
                            1 a
                            2 bba
                            3 ca
                            5 dda
                            6 Eda
                            1 a6 rows selectedSQL> select (select a2 from a where a1=b1) from b
  2  ;(SELECTA2FROMAWHEREA1=B1)
-------------------------
ba
ca6 rows selectedSQL>

Answer 1

你完全可以使用联合查询或是join的

Answer 2

首先ID 和 FID 是是相同类型字符型
select a.name as 行业类别,b.name as 行业名称 
from a a,a b 
where a.id = b.fid(+) and length(a.id) = 2 and length(b.id) <> 2

Answer 3

修改一下：
select a.name as 行业类别,b.name as 行业名称 
from a a,a b 
where a.id = b.fid and length(a.id) = 2 and length(b.id) <> 2