Oracle hierarchy data representation ambiguity - oracle10g

Question

I am having a table in following structure.
_________________________________
|| ExpObjkey Exp1 Exp2 operator||
________________________________
1 2 3 +
2 4 5 +
3 6 7 -
I want to have records in the following order:
for expObjKey=1, we will have
ExpObjKey Expression
1 (4+5)+(6-7)
explanation:
for ExpObjKey 1 we will have 2 +3
then 2 will have 4+5
and 3 will have 6+7.
Its more like a hierarchy.
I have tried lots of possible ways but no near the solution.
SELECT expObjkey, SYS_CONNECT_BY_PATH(exp1||' ' ||operator|| exp2||')', ' ( ') "Path"
FROM bpmn_expression
CONNECT BY PRIOR
exp1=expObjkey or exp2=expObjkey
start with expObjkey=1

Answer 1

I don't think you can do this with a hierarchical query, but I'd be interested to be proven wrong. You'd need to start at the bottom of the tree and work your way up to allow the substitutions to happen; but then there doesn't seem to be a way to combine the partial expressions that produces. It might be possible with recursive subquery factoring, but that isn't available until 11gR2.
On 10g you could use your own recursive function to generate what you need:
create or replace function get_expression(p_key bpmn_expression.expobjkey%type)
return varchar2 is
row bpmn_expression%rowtype;
begin
select * into row from bpmn_expression where expobjkey = p_key;
return '(' || get_expression(row.exp1)
|| row.operator || get_expression(row.exp2) || ')';
exception
when no_data_found then
return to_char(p_key);
end;
/
select get_expression(1) as expression from dual;
EXPRESSION
------------------------------
((4+5)+(6-7))
SQL Fiddle.
You can strip the outer parentheses with trim or regexp_replace if you want to, but they may be acceptable.
If you add another layer, say a record with values 7, 8, 9, '*', this would give:
EXPRESSION
------------------------------
((4+5)+(6-(8*9)))
SQL Fiddle.
But this isn't going to be very efficient against a large data set, since it will do a lot of single-row look-ups.