Oracle SQL中使用递归查询的有向图只访问每个节点一次

为了避免遍历算法返回已访问的边,确实可以将访问的边保留在某个位置。正如您已经发现的那样,使用字符串连接不会取得多大成功。然而,还有其他可用的“值串联”技术。。。

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

1. 我将有向图预处理为无向图 union
2. 我记得几年前在Oracle 11.2上尝试过这样的东西。我记得它失败了,尽管我不记得为什么。在12.2版本,它运行正常。只需在11g上试一试;我没有可用的。
4. 正如您可能从我的评论中理解的那样,您必须自己解决所需的订购问题。:-)

将重新访问的边限制为零

请帮忙?

arr_output l_visited_nodes .你有多种选择,明智地选择。

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;

/

A 考虑到图是无向的。。。

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

1. 再说一次,我没有做出任何努力来保持你所要求的订单,因为你说这没那么重要。
2. 这是对 edge 桌子与具有冗余边缘访问的纯SQL解决方案相比,这可能对性能造成更大的影响,也可能不会。适当测试更多解决方案,看看哪一个最适合你。
3. 这段特殊的代码将适用于12c及更高版本。对于11g及以下,您必须申报 rec_output 和 arr\U输出