Oracle tree计算叶子节点到根节点的乘积

//有下面一棵二叉树，转换为表结构:   
parent_id  child_id  weight   
------     -------   ------   
a          b              2    
b          c              3   
c          d              4   
b          e              7   
c          f              2   
//计算叶子节点到根节点之间边的权值的乘积:   
leaf weight   
---- ------   
d        24   
e        14   
f        12   
//数据   
create table tree (parent_id varchar2(10),child_id varchar2(10),weight number(2));   
insert into tree values('a','b',2);   
insert into tree values('b','c',3);   
insert into tree values('c','d',4);   
insert into tree values('b','e',7);   
insert into tree values('c','f',2);   
//创建一个函数实现求字串乘积(动态SQL)   
create or replace function func_tree(str in varchar2)   
return number   
as  
  num number;   
begin   
     execute immediate 'select '||str||' from dual' into num;   
     return num;   
end func_tree;   
//sql代码:   
select child_id, func_tree(substr(sys_connect_by_path(weight, '*'), 2)) weight   
from tree t   
where connect_by_isleaf = 1   
start with not exists (select 1 from tree where t.parent_id=child_id)   
connect by prior child_id = parent_id   
order by child_id;   
//结果:   
CHILD_ID       WEIGHT   
---------- ----------   
d                  24   
e                  14   
f                  12 

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