我希望所有国家/地区都与指定国家/地区的N（1,2,3,4 ......）边界隔开。
N也应该被指定。
例如，我有“border”和“country”表：
border | neighbor ----------------- FR | DE FR | IT IT | FR DE | FR DE | PL PL | DE DE | DK DK | DE CODE COUNTRYNAME ---- --------- FR France DE Germany RU Russia IT Italy PL Poland DK Denmark
如果我希望将国家与法国分开2个边界，则应返回波兰（FR - > DE - > PL）和丹麦（FR - > DE - > DK）
如果我想让国家与法国分开一个边界，那么它应该返回德国（FR - > DE）和意大利（FR - > IT）
如果需要，我可以修改边框。
我尝试了一些分层查询但没有成功。
由于 BR
答案 0 :(得分：8)
以下是所有可能路径及其长度的完整列举，给出了一个起始国家，并且没有限制路径是两个国家之间的最短路径（免责声明，不要在太多国家/地区运行）：
WITH
countries AS (SELECT DISTINCT border country FROM t),
chains (country, path, destination, steps) AS (
SELECT country, country, country, 0
FROM countries
UNION ALL
SELECT chains.country, chains.path || '->' || t.neighbor, t.neighbor, chains.steps + 1
FROM chains
JOIN t ON chains.destination = t.border
AND chains.path NOT LIKE '%' || t.neighbor || '%' -- This prevents cycles
)
SELECT *
FROM chains
ORDER BY country, steps;
结果是：
| COUNTRY | PATH | DESTINATION | STEPS |
|---------|----------------|-------------|-------|
| DE | DE | DE | 0 |
| DE | DE->PL | PL | 1 |
| DE | DE->FR | FR | 1 |
| DE | DE->DK | DK | 1 |
| DE | DE->FR->IT | IT | 2 |
| DK | DK | DK | 0 |
| DK | DK->DE | DE | 1 |
| DK | DK->DE->FR | FR | 2 |
| DK | DK->DE->PL | PL | 2 |
| DK | DK->DE->FR->IT | IT | 3 |
| FR | FR | FR | 0 |
| FR | FR->IT | IT | 1 |
| FR | FR->DE | DE | 1 |
| FR | FR->DE->DK | DK | 2 |
| FR | FR->DE->PL | PL | 2 |
| IT | IT | IT | 0 |
| IT | IT->FR | FR | 1 |
| IT | IT->FR->DE | DE | 2 |
| IT | IT->FR->DE->PL | PL | 3 |
| IT | IT->FR->DE->DK | DK | 3 |
| PL | PL | PL | 0 |
| PL | PL->DE | DE | 1 |
| PL | PL->DE->FR | FR | 2 |
| PL | PL->DE->DK | DK | 2 |
| PL | PL->DE->FR->IT | IT | 3 |
将查询存储在视图中，然后您可以对其进行过滤，例如
SELECT * FROM my_view WHERE country = 'FR' AND steps = 2
如果您确实需要两个国家/地区之间的最短路径，请重复使用 当两条路径相关时，该视图再次选择一条任意路径（同样，这不是最有效的解决方案，不要为太多国家做到这一点！）：
SELECT
country,
destination,
MIN(steps) KEEP (DENSE_RANK FIRST ORDER BY steps) AS steps,
MIN(path) KEEP (DENSE_RANK FIRST ORDER BY steps) AS path
FROM paths
WHERE country != destination
GROUP BY country, destination
ORDER BY country, destination
得到：
| COUNTRY | DESTINATION | STEPS | PATH |
|---------|-------------|-------|----------------|
| DE | DK | 1 | DE->DK |
| DE | FR | 1 | DE->FR |
| DE | IT | 2 | DE->FR->IT |
| DE | PL | 1 | DE->PL |
| DK | DE | 1 | DK->DE |
| DK | FR | 2 | DK->DE->FR |
| DK | IT | 3 | DK->DE->FR->IT |
| DK | PL | 2 | DK->DE->PL |
| FR | DE | 1 | FR->DE |
| FR | DK | 2 | FR->DE->DK |
| FR | IT | 1 | FR->IT |
| FR | PL | 2 | FR->DE->PL |
| IT | DE | 2 | IT->FR->DE |
| IT | DK | 3 | IT->FR->DE->DK |
| IT | FR | 1 | IT->FR |
| IT | PL | 3 | IT->FR->DE->PL |
| PL | DE | 1 | PL->DE |
| PL | DK | 2 | PL->DE->DK |
| PL | FR | 2 | PL->DE->FR |
| PL | IT | 3 | PL->DE->FR->IT |
答案 1 :(得分：4)
您可以将每个国家/地区的邻居聚合到一个集合中，然后使用简单的分层查询来查找（非循环）路径：
Oracle 11g R2架构设置：
create table borders (border char(2), neighbor char(2));
insert into borders values ('FR','DE');
insert into borders values ('FR','IT');
insert into borders values ('IT','FR');
insert into borders values ('DE','FR');
insert into borders values ('DE','PL');
insert into borders values ('PL','DE');
insert into borders values ('DE','DK');
insert into borders values ('DK','DE');
insert into borders values ('RU','PL');
insert into borders values ('PL','RU');
insert into borders values ('IT','CH');
insert into borders values ('FR','CH');
insert into borders values ('DE','CH');
insert into borders values ('CH','IT');
insert into borders values ('CH','FR');
insert into borders values ('CH','DE');
CREATE TYPE countrylist AS TABLE OF CHAR(2);
查询1 ：
WITH neighbors ( country, neighbors ) AS (
SELECT border,
CAST( COLLECT( neighbor ) AS COUNTRYLIST )
FROM borders
GROUP BY border
)
SELECT SYS_CONNECT_BY_PATH( country, '->' ) AS path,
CONNECT_BY_ROOT( country ) AS origin,
country AS destination,
LEVEL - 1 AS path_length
FROM neighbors
WHERE LEVEL - 1 = 4 -- Remove this to find paths of any length
START WITH country = 'FR' -- Remove this to start from any country
CONNECT BY NOCYCLE
country MEMBER OF PRIOR neighbors
<强> Results ：
| PATH | ORIGIN | DESTINATION | PATH_LENGTH |
|----------------------|--------|-------------|-------------|
| ->FR->CH->DE->PL->RU | FR | RU | 4 |
| ->FR->IT->CH->DE->DK | FR | DK | 4 |
| ->FR->IT->CH->DE->PL | FR | PL | 4 |
解释计划：
-----------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost | Time |
-----------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 16 | 608 | 5 | 00:00:01 |
| * 1 | FILTER | | | | | |
| * 2 | CONNECT BY NO FILTERING WITH START-WITH | | | | | |
| 3 | VIEW | | 16 | 608 | 4 | 00:00:01 |
| 4 | SORT GROUP BY | | 16 | 128 | 4 | 00:00:01 |
| 5 | TABLE ACCESS FULL | BORDERS | 16 | 128 | 3 | 00:00:01 |
-----------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
------------------------------------------
* 1 - filter(LEVEL-1=4)
* 2 - filter("COUNTRY"MEMBER OFPRIOR "NEIGHBORS" AND "COUNTRY"='FR')
查询2 这将获得成对国家/地区之间的最短路径（带有联系）：
WITH neighbors ( country, neighbors ) AS (
SELECT border,
CAST( COLLECT( neighbor ) AS COUNTRYLIST )
FROM borders
GROUP BY border
)
SELECT path,
origin,
destination,
path_length
FROM (
SELECT SYS_CONNECT_BY_PATH( country, '->' ) AS path,
CONNECT_BY_ROOT( country ) AS origin,
country AS destination,
LEVEL - 1 AS path_length,
RANK() OVER (
PARTITION BY CONNECT_BY_ROOT( country ), country
ORDER BY LEVEL ASC
) AS path_length_rank
FROM neighbors
WHERE LEVEL > 1
CONNECT BY NOCYCLE
country MEMBER OF PRIOR neighbors
ORDER BY origin, destination
)
WHERE path_length_rank = 1
<强> Results ：
| PATH | ORIGIN | DESTINATION | PATH_LENGTH |
|----------------------|--------|-------------|-------------|
| ->CH->DE | CH | DE | 1 |
| ->CH->DE->DK | CH | DK | 2 |
| ->CH->FR | CH | FR | 1 |
| ->CH->IT | CH | IT | 1 |
| ->CH->DE->PL | CH | PL | 2 |
| ->CH->DE->PL->RU | CH | RU | 3 |
| ->DE->CH | DE | CH | 1 |
| ->DE->DK | DE | DK | 1 |
| ->DE->FR | DE | FR | 1 |
| ->DE->FR->IT | DE | IT | 2 |
| ->DE->CH->IT | DE | IT | 2 |
| ->DE->PL | DE | PL | 1 |
| ->DE->PL->RU | DE | RU | 2 |
| ->DK->DE->CH | DK | CH | 2 |
| ->DK->DE | DK | DE | 1 |
| ->DK->DE->FR | DK | FR | 2 |
| ->DK->DE->FR->IT | DK | IT | 3 |
| ->DK->DE->CH->IT | DK | IT | 3 |
| ->DK->DE->PL | DK | PL | 2 |
| ->DK->DE->PL->RU | DK | RU | 3 |
| ->FR->CH | FR | CH | 1 |
| ->FR->DE | FR | DE | 1 |
| ->FR->DE->DK | FR | DK | 2 |
| ->FR->IT | FR | IT | 1 |
| ->FR->DE->PL | FR | PL | 2 |
| ->FR->DE->PL->RU | FR | RU | 3 |
| ->IT->CH | IT | CH | 1 |
| ->IT->FR->DE | IT | DE | 2 |
| ->IT->CH->DE | IT | DE | 2 |
| ->IT->CH->DE->DK | IT | DK | 3 |
| ->IT->FR->DE->DK | IT | DK | 3 |
| ->IT->FR | IT | FR | 1 |
| ->IT->CH->DE->PL | IT | PL | 3 |
| ->IT->FR->DE->PL | IT | PL | 3 |
| ->IT->FR->DE->PL->RU | IT | RU | 4 |
| ->IT->CH->DE->PL->RU | IT | RU | 4 |
| ->PL->DE->CH | PL | CH | 2 |
| ->PL->DE | PL | DE | 1 |
| ->PL->DE->DK | PL | DK | 2 |
| ->PL->DE->FR | PL | FR | 2 |
| ->PL->DE->CH->IT | PL | IT | 3 |
| ->PL->DE->FR->IT | PL | IT | 3 |
| ->PL->RU | PL | RU | 1 |
| ->RU->PL->DE->CH | RU | CH | 3 |
| ->RU->PL->DE | RU | DE | 2 |
| ->RU->PL->DE->DK | RU | DK | 3 |
| ->RU->PL->DE->FR | RU | FR | 3 |
| ->RU->PL->DE->FR->IT | RU | IT | 4 |
| ->RU->PL->DE->CH->IT | RU | IT | 4 |
| ->RU->PL | RU | PL | 1 |
解释计划：
---------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost | Time |
---------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 16 | 32576 | 6 | 00:00:01 |
| * 1 | VIEW | | 16 | 32576 | 6 | 00:00:01 |
| 2 | SORT ORDER BY | | 16 | 608 | 6 | 00:00:01 |
| * 3 | WINDOW SORT PUSHED RANK | | 16 | 608 | 6 | 00:00:01 |
| * 4 | FILTER | | | | | |
| * 5 | CONNECT BY WITHOUT FILTERING | | | | | |
| 6 | VIEW | | 16 | 608 | 4 | 00:00:01 |
| 7 | SORT GROUP BY | | 16 | 128 | 4 | 00:00:01 |
| 8 | TABLE ACCESS FULL | BORDERS | 16 | 128 | 3 | 00:00:01 |
---------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
------------------------------------------
* 1 - filter("PATH_LENGTH_RANK"=1)
* 3 - filter(RANK() OVER ( PARTITION BY ANY,"COUNTRY" ORDER BY LEVEL)<=1)
* 4 - filter(LEVEL>1)
* 5 - filter("COUNTRY"MEMBER OFPRIOR "NEIGHBORS")
答案 2 :(得分：3)
您的BORDERS表包含互惠关系（例如FR->DE，DE->FR）。这意味着您需要处理周期。这根本不是直截了当的，因为你想避免在三度分离时说FR->DE->PL->DE。
我这里有一个递归的WITH子句，（所以Oracle 11gR2或更高版本）就是这样做的。
with hqry (path, nghbr, prev_bdr, root_bdr, lvl) as (
select b.border
, b.neighbor
, b.border
, b.border
, 1 as lvl
from borders b
where b.border = 'FR'
union all
select hqry.path || '->' || b.border
, b.neighbor
, hqry.nghbr
, hqry.root_bdr
, hqry.lvl + 1
from hqry
join borders b on b.border = hqry.nghbr
where b.neighbor != hqry.root_bdr
and b.neighbor != hqry.prev_bdr
and hqry.lvl < 3 -- this is a nasty kludge, with more time I'd like to fix it
)
SEARCH DEPTH FIRST BY path SET order1
CYCLE path SET cycle TO 1 DEFAULT 0
select path || '->' || nghbr as end_path
from hqry
where hqry.lvl = 3
;
需要五个参数
path - 上一个边框链nghbr - 当前的邻居，说明根国家，即法国prev_bdr - 阻止FR->DE->PL->DE root_bdr - 阻止FR->CH->IT->FR lvl - 跟踪分离度三种分离度的样本输出：
FR->CH->DE->DK
FR->CH->DE->PL
FR->DE->CH->IT
FR->DE->PL->RU
FR->IT->CH->DE
有here。我在几个国家补充道：瑞士增加了一些令人讨厌的边缘案例。
显然上面的输出显示它没有强制执行a SQL Fiddle demo here，这是留给读者的练习:)如果你有兴趣添加它 - 你应该是，因为我认为这是关键一个强大的解决方案 - 我建议你真实shortest path algorithm。
答案 3 :(得分：0)
您可以使用CONNECT_BY_ROOT查找邻居并按LEVEL过滤以查找第n个邻居。
SELECT *
FROM (
SELECT border
,connect_by_root(neighbor) AS neighbor
FROM borders
WHERE border = :ctry
AND LEVEL = :n
CONNECT BY NOCYCLE
PRIOR border = neighbor
) WHERE neighbor != :ctry