Question

如何使用connect by获取层次结构的顶部和底部，我有一个存储id之间转换的表（ID-> REPLACE_ID），我有兴趣从任何id开始获取最新的id。< / p>

--drop table test_connect_by;
create table test_connect_by(ID number, REPLACE_ID NUMBER);
insert into test_connect_by values(1,2);
insert into test_connect_by values(2,3);
insert into test_connect_by values(3,4);

insert into test_connect_by values(51,52);
insert into test_connect_by values(52,53);
insert into test_connect_by values(53,54);
insert into test_connect_by values(55,55);

SELECT id,replace_id, level
   FROM test_connect_by
   START WITH ID in (1,51)
   CONNECT BY PRIOR replace_id = id;

我有兴趣从1-4和51-54获得转换，或者我可以从2开始并获得2-4。有什么我可以分组来识别以1开头的组和以51开头的组吗？

Answer 1

未经测试，因此可能存在一些错误：

select id, replace_id 
from (
    SELECT CONNECT_BY_ROOT id as id, replace_id
         , row_number() over (partition by CONNECT_BY_ROOT id order by level desc) as rn
    FROM test_connect_by
    START WITH ID in (1,51)
    CONNECT BY PRIOR replace_id = id
) as T 
where rn = 1

Answer 2

作为一种（更直接）的方法，您可以简单地找到id值的最低replace_id和最高connect_by_root()分组，如果replace_id始终保证更高而不是id，否则请参阅Lennart answer：

select min(id)         as begins
     , max(replace_id) as ends
  from test_connect_by
 start with id in (1, 51)
 connect by id = prior replace_id
 group by connect_by_root(id)

结果：

    BEGINS       ENDS
---------- ----------
         1          4
        51         54

Oracle Connect按顶部/底部层次结构

2 个答案: