Connect by prior repeating nodes

Question

I have a hierarchical structure (a directed acyclic graph with a root node) and I want to list only the leaf nodes for a root node. For example, say I have the following graph
A -> B, A->C, A->D
B->C,
C->D,
D->E,
D->F
I want to get the results as A ->E, A->F
Queries to create the above graph
create table test_hierarchy (parent varchar2(10), child varchar2(10));
insert into test_hierarchy (parent, child) values ('a','b');
insert into test_hierarchy (parent, child) values ('a','c');
insert into test_hierarchy (parent, child) values ('a','d');
insert into test_hierarchy (parent, child) values ('b','c');
insert into test_hierarchy (parent, child) values ('b','d');
insert into test_hierarchy (parent, child) values ('c','d');
insert into test_hierarchy (parent, child) values ('d','e');
insert into test_hierarchy (parent, child) values ('d','f');
To achieve the desired output i have written the following query
Select connect_by_root(parent), child from test_hierarchy where connect_by_isleaf = 1
start with parent = 'a'
connect by prior child = parent
But I get the result set with A->E and A->F repeated 6 times from all the possible paths.
This is making the whole operation very slow in the production env. Adding distinct is making it even slower.
Is there a way for me to specify to the db to not traversed the already traversed paths.
Any help is highly appreciated

Answer 1

Hi,
[email protected] wrote:
Thanks ... but as far as I know the recursive with clause is supported only in Oracle 11g. And my client is using Oracle 10g. Also, I have not tried this on oracle 11g instance but I am assuming that the output and query you wrote below is for oracle only.
Also, as per Franks suggestion; I did some reading on pipelined functions. Basically, I tried creating a function (not pipelined) that will take a collection and a string. The function would update the collection to have this string if it is not present already in the collection. And would return true if the collection gets modified, false otherwise.
But now am stuck because i cannot call this function in sql query as it has an out parameter. Functions that have OUT parameters, or that return data types not found in SQL (even BOOLEAN), can only be called from PL/SQL. They can not be used in SQL statements, even SQL statements embedded in PL/SQL.
I suggest a function that takes one IN-argument, a string (such as 'A'), that returns a delimited string (such as 'E,F'). You could split that string into parts after it was returned, if necessary.
So you might call the function in a SQL statment like this:
SELECT  get_leaves ('A')
FROM    my_table;and it would display
GET_LEAVES
E,FInside get_leaves, you can use whatever other functions yu want, including functions with user-defined arguments and return values. (OUT arguments in functions are not very good programming, but they would be allowed, if you really want them.)
It's only inside get_leaves that you need to keep track of what nodes have been visited already; the calling program doesn't need to see that part of the job at all.