Bar*_*ard 6 sql recursive-query common-table-expression oracle11g
描述
在我们的问题域中,我们正在研究一组连接在一起形成图形的边.从给定节点(或节点)开始,我们必须列出整个图中连接到给定节点(或节点)的所有链接.我们必须从左到右,从上到下显示这些链接.
对于具有有限循环次数的图形,我们对此问题有一个有效的查询.较多的循环会以指数方式增加执行时间.
我们需要在递归期间限制对同一节点的访问以获得有效的解决方案.
下面的示例只包含一个循环,但是这个循环已经导致了86个额外的和过时的行.
在类似的帖子中,使用ROW和ANY运算符为postgresql提供了解决方案,但我找不到Oracle解决方案.
我们正在寻找替代解决方案或限制访问相同边缘的方式.
任何帮助是极大的赞赏!
类似
使用递归查询访问有向图就好像它是一个无向图,在postgresql中提供了一个解决方案.我们需要使用Oracle11g.
例
边缘
A-B, B-D, C-A, C-E, C-F, H-F, E-B, G-D, G-I
图形
A
/ \
C - E - B - D
\ /
H - F G - I
DDL和DML
CREATE TABLE EDGE (
FROM_ID VARCHAR(10),
TO_ID VARCHAR(10)
);
INSERT INTO EDGE VALUES ('A', 'B');
INSERT INTO EDGE VALUES ('E', 'B');
INSERT INTO EDGE VALUES ('C', 'E');
INSERT INTO EDGE VALUES ('C', 'A');
INSERT INTO EDGE VALUES ('C', 'F');
INSERT INTO EDGE VALUES ('B', 'D');
INSERT INTO EDGE VALUES ('G', 'D');
INSERT INTO EDGE VALUES ('H', 'F');
INSERT INTO EDGE VALUES ('G', 'I');
输入
nodes: 'A'
要求的输出
C A
C E
C F
H F
A B
E B
B D
G D
G I
现行解决方案
我们当前的解决方案正是我们所需要的,但如上所述,每个额外的循环都会以指数方式增加执行时间.
SELECT
c.LVL,
c.FROM_ID,
c.TO_ID,
CASE
WHEN lag(C.TO_ID)
OVER (
PARTITION BY C.LVL
ORDER BY C.LVL, C.TO_ID ) = C.TO_ID
THEN C.LVL || '-' || C.TO_ID
WHEN lead(C.TO_ID)
OVER (
PARTITION BY C.LVL
ORDER BY C.LVL, C.TO_ID ) = C.TO_ID
THEN C.LVL || '-' || C.TO_ID
ELSE C.LVL || '-' || C.FROM_ID
END GROUP_ID
FROM (
WITH chain(LVL, FROM_ID, TO_ID ) AS (
SELECT
1 LVL,
root.FROM_ID FROM_ID,
root.TO_ID TO_ID
FROM EDGE root
WHERE root.TO_ID IN (:nodes)
OR (root.FROM_ID IN (:nodes) AND NOT EXISTS(
SELECT *
FROM EDGE
WHERE TO_ID IN (:nodes)
))
UNION ALL
SELECT
LVL +
CASE
WHEN previous.TO_ID = the_next.FROM_ID
THEN 1
WHEN previous.TO_ID = the_next.TO_ID
THEN 0
WHEN previous.FROM_ID = the_next.FROM_ID
THEN 0
ELSE -1
END LVL,
the_next.FROM_ID FROM_ID,
the_next.TO_ID TO_ID
FROM EDGE the_next
JOIN chain previous ON previous.TO_ID = the_next.FROM_ID
OR the_next.TO_ID = previous.FROM_ID
OR (previous.TO_ID = the_next.TO_ID AND previous.FROM_ID <> the_next.FROM_ID)
OR (previous.TO_ID <> the_next.TO_ID AND previous.FROM_ID = the_next.FROM_ID)
)
SEARCH BREADTH FIRST BY FROM_ID SET ORDER_ID
CYCLE FROM_ID, TO_ID SET CYCLE TO 1 DEFAULT 0
SELECT
C.*,
row_number()
OVER (
PARTITION BY LVL, FROM_ID, TO_ID
ORDER BY ORDER_ID ) rank
FROM chain C
ORDER BY LVL, FROM_ID, TO_ID
) C
WHERE C.rank = 1;
为了防止遍历算法返回到已经访问过的边缘，确实可以将访问过的边缘保留在某处。正如您已经发现的，字符串连接不会取得太大成功。然而，还有其他可用的“值串联”技术......
您必须有一个方便的模式级标量集合可供您使用：
create or replace type arr_strings is table of varchar2(64);
然后您可以在每次迭代中将访问过的边收集到该集合中：
with nondirected$ as (
select from_id, to_id, from_id||'-'||to_id as edge_desc
from edge
where from_id != to_id
union all
select to_id, from_id, from_id||'-'||to_id as edge_desc
from edge
where (to_id, from_id) not in (
select from_id, to_id
from edge
)
),
graph$(lvl, from_id, to_id, edge_desc, visited_edges) as (
select 1, from_id, to_id, edge_desc,
arr_strings(edge_desc)
from nondirected$ R
where from_id in (&nodes)
--
union all
--
select
lvl+1,
Y.from_id, Y.to_id, Y.edge_desc,
X.visited_edges multiset union arr_strings(Y.edge_desc)
from graph$ X
join nondirected$ Y
on Y.from_id = X.to_id
where not exists (
select 1
from table(X.visited_edges) Z
where Y.edge_desc = Z.column_value
)
)
search breadth first by edge_desc set order_id
cycle edge_desc set is_cycle to 1 default 0,
ranked_graph$ as (
select C.*,
row_number() over (partition by edge_desc order by lvl, order_id) as rank$
from graph$ C
-- where is_cycle = 0
)
select *
from ranked_graph$
--where rank$ <= 1
order by lvl, order_id
;
笔记
union我通过将一组反向边添加到输入来将有向图预处理为无向图。这应该会使递归遍历谓词更容易阅读。仅仅是为了更轻松地读取和编写 SQL。当然，你不必这样做。将重新访问的边缘限制为零
在 SQL 中，你不能。你提到的 PostgreSQL 解决方案确实可以做到这一点。但在 Oracle 中，您不能这样做。对于每个遍历连接，您必须测试所有其他遍历连接的行。这意味着某种聚合或分析......Oracle 禁止并抛出 ORA 异常。
PLSQL 来救援？
不过，您可以在 PL/SQL 中完成此操作。它应该有多少性能，取决于您想要花费多少内存从数据库预取边缘，以及您愿意从“当前”节点遍历图形的 SQL 往返次数，或者您是否愿意使用与如果您宁愿反连接常规arr_output集合相比，甚至需要更多内存将访问的节点保留在奇特的按边索引集合中l_visited_nodes。你有多种选择，明智地选择。
无论如何，对于大量使用 SQL 引擎的最简单场景，这可能是您正在寻找的代码......
create or replace
package pkg_so_recursive_traversal
is
type rec_output is record (
from_id edge.from_id%type,
to_id edge.to_id%type,
lvl integer
);
type arr_output is table of rec_output;
function traverse_a_graph
( i_from in arr_strings
, i_is_directed in varchar2 default 'NO' )
return arr_output
pipelined;
end pkg_so_recursive_traversal;
/
create or replace
package body pkg_so_recursive_traversal
is
function traverse_a_graph
( i_from in arr_strings
, i_is_directed in varchar2 )
return arr_output
pipelined
is
l_next_edges arr_output;
l_current_edges arr_output;
l_visited_edges arr_output := arr_output();
l_out rec_output;
i pls_integer;
l_is_directed varchar2(32) := case when i_is_directed = 'YES' then 'YES' else 'NO' end;
begin
select E.from_id, E.to_id, 0
bulk collect into l_next_edges
from table(i_from) F
join edge E
on F.column_value in (E.from_id, case when l_is_directed = 'YES' then null else E.to_id end)
where E.from_id != E.to_id;
l_out.lvl := 0;
loop
dbms_output.put_line(l_next_edges.count());
exit when l_next_edges.count() <= 0;
l_out.lvl := l_out.lvl + 1;
-- spool the edges to output
i := l_next_edges.first();
while i is not null loop
l_out.from_id := l_next_edges(i).from_id;
l_out.to_id := l_next_edges(i).to_id;
pipe row(l_out);
i := l_next_edges.next(i);
end loop;
l_current_edges := l_next_edges;
l_visited_edges := l_visited_edges multiset union l_current_edges;
-- find next edges
select unique E.from_id, E.to_id, 0
bulk collect into l_next_edges
from table(l_current_edges) CE
join edge E
on CE.to_id in (E.from_id, case when l_is_directed = 'YES' then null else E.to_id end)
or l_is_directed = 'NO' and CE.from_id in (E.from_id, E.to_id)
where E.from_id != E.to_id
and not exists (
select 1
from table(l_visited_edges) VE
where VE.from_id = E.from_id
and VE.to_id = E.to_id
);
end loop;
return;
end;
end pkg_so_recursive_traversal;
/
当调用 的起始节点A并考虑该图是无向的时......
select *
from table(pkg_so_recursive_traversal.traverse_a_graph(
i_from => arr_strings('A'),
i_is_directed => 'NO'
));
...它产生...
FROM_ID TO_ID LVL
---------- ---------- ----------
A B 1
C A 1
C E 2
B D 2
C F 2
E B 2
G D 3
H F 3
G I 4
笔记
edge。与具有冗余边缘访问的纯 SQL 解决方案相比，这可能会对性能产生更大的影响，也可能不会。正确测试更多解决方案，看看哪一种最适合您。rec_output和类型。arr_output