Oracle SQL左连接同一表的次数未知

您正在寻找的是一个递归查询。像这样的东西：

with cte (old, new, lev) as(  select old, new, 1 as lev from mytable  union all  select m.old, cte.new, cte.lev + 1  from mytable m  join cte on cte.old = m.new)select old, max(new) keep (dense_rank last order by lev) as newfrom ctegroup by oldorder by old;

递归CTE创建所有迭代（您可以通过将查询替换为来查看此迭代

select * fromcte

new

old

KEEP LAST

Rextester演示：http
://rextester.com/CHTG34988