两表关联问题

[realx]

我想根据两个表的ROWNUM进行外联结，最好只用一条SQL语句实现。比如有A,B两表，当A表的记录数比B表多时，达到A=B(+)的效果，当A表的记录数比B表少时达到A(+)=B的效果。

[adaizi1980]

select a_id,... from
( select a_id,b_id,... from
(select a.rownum as a_id,... from a ) as A1,
(select b.rownum as b_id,... from a ) as B1
where A1.a_id = B1.b_id(+)
)

union all

select b_id,... from
( select a_id,b_id,... from
(select a.rownum as a_id,... from a ) as A1,
(select b.rownum as b_id,... from a ) as B1
where B1.b_id = A1.a_id(+)
and not exists
( select 1 from
( select a_id,b_id,... from
(select a.rownum as a_id,... from a ) as A1,
(select b.rownum as b_id,... from a ) as B1
where A1.a_id = B1.b_id(+)
) XX where XX.a_id = B1.b_id
)
)