How to gather hierarchical data items and build a tree considering their dependencies - sql

Question

There is a table containing hierarchical data, e.g.:
| table "attribute_instances" |
+----+----------+------------+---------------+----------+
| id | tree_ref | parent_ref | attribute_ref | data_ref |
+----+----------+------------+---------------+----------+
| 1 | 1 | -1 | 1 | 1 |
| 2 | 1 | 1 | 2 | 2 |
| 3 | 2 | -1 | 1 | 3 |
| 4 | 2 | 3 | 2 | 2 |
It contains many separate trees (see tree_ref), each of them instantiating some attributes (see attribute_ref) and have a data reference data_reference, where data might be referenced in other trees, too.
Now, those trees should be merged into a single tree, in which (by now) up to 5 attributes may be chosen as level for that tree, e.g.:
attribute => level
------------------
2 => 1
1 => 2
What I need is one or more queries, that collects the data from table attribute_instances and gives a result as follows:
| table "merged_attribute_instances" |
+----+------------+---------------+----------+
| id | parent_ref | attribute_ref | data_ref |
| 5 | -1 | 2 | 2 |
| 6 | 5 | 1 | 1 |
| 7 | 5 | 1 | 3 |
This is the desired merged tree:
id:5 - data_ref:2
id:6 - data_ref:1
id:7 - data_ref:3
Note, that attribute_ref = 2 occurs only once in the resulting tree, as all instances of it have same data_ref value (that is 2).
I've tried some joins like
select *
from attribute_instances a
join attribute_instances b on a.tree_ref = b.tree_ref
But that seems to me being bad for having user-defined tree depth. I'm sure there is a better solution.
UPDATE: I should add, that table merged_attribute_instances is a temporary table. And the collecting query is iterated with for..do. In the loop the collected attribute_instances are then added to the temporary table.

Answer 1

OK, then use this:
SET TERM ^ ;
create or alter procedure GETTREENODES
returns (
ID integer,
TREE_REF integer,
PARENT_REF integer,
ATTRIBUTE_REF integer,
DATA_REF integer)
as
declare variable DATAREFEXISTS varchar(4096);
begin
DATAREFEXISTS = ',';
for
Select id, tree_ref, parent_ref, attribute_ref, data_ref from attribute_instances
into :id, :tree_ref, :parent_ref, :attribute_ref, :data_ref
do begin
IF (position(',' || data_ref || ',', DATAREFEXISTS) =0) THEN
begin
suspend;
DATAREFEXISTS = DATAREFEXISTS || data_ref || ',' ;
end
end
end^
SET TERM ; ^
/* Following GRANT statetements are generated automatically */
GRANT SELECT ON ATTRIBUTE_INSTANCES TO PROCEDURE GETTREENODES;
/* Existing privileges on this procedure */
GRANT EXECUTE ON PROCEDURE GETTREENODES TO SYSDBA;
Call it like this:
Select * from gettreenodes
order by tree_ref, parent_ref