Hi,
I'm playing with the new "WITH RECURSIVE" feature of 8.4. I'm trying to
figure out how to use it with trees.
Here is the test code I use:
---------------------------------------------------------
--DROP TABLE recursion;
CREATE TABLE recursion
( id serial, lookup varchar(16), parent_id integer, primary key(id), foreign key(parent_id) references recursion(id)
);
INSERT INTO recursion VALUES(1, 'a1', NULL);
INSERT INTO recursion VALUES(2, 'b11', 1);
INSERT INTO recursion VALUES(645, 'c111', 2);
INSERT INTO recursion VALUES(823, 'c112', 2);
INSERT INTO recursion VALUES(243, 'c113', 2);
INSERT INTO recursion VALUES(6, 'b12', 1);
INSERT INTO recursion VALUES(845, 'c121', 6);
INSERT INTO recursion VALUES(583, 'c122', 6);
INSERT INTO recursion VALUES(9, 'b13', 1);
INSERT INTO recursion VALUES(10, 'c131', 9);
WITH RECURSIVE parse_tree (depth, id, lookup, parent_id) AS
( SELECT 0, parent.id, parent.lookup, parent.parent_id FROM recursion AS parent WHERE parent_id IS NULL
UNIONALL SELECT parent.depth + 1, child.id, child.lookup, child.parent_id FROM parse_tree parent,
recursionAS child WHERE child.parent_id = parent.id
)
SELECT * FROM parse_tree;
---------------------------------------------------------
Here is the result:
depth | id | lookup | parent_id
-------+-----+--------+----------- 0 | 1 | a1 | 1 | 2 | b11 | 1 1 | 6 | b12 |
1 1 | 9 | b13 | 1 2 | 645 | c111 | 2 2 | 823 | c112 | 2 2 | 243 | c113 |
2 2 | 845 | c121 | 6 2 | 583 | c122 | 6 2 | 10 | c131 | 9
I'd like to perform a real recursion, and show the tree structure in a
more appopriate way, like this:
depth | id | lookup | parent_id
-------+-----+--------+----------- 0 | 1 | a1 | 1 | 2 | b11 | 1 2 | 645 | c111 |
2 2 | 823 | c112 | 2 2 | 243 | c113 | 2 1 | 6 | b12 | 1 2 | 845 | c121 |
6 2 | 583 | c122 | 6 1 | 9 | b13 | 1 2 | 10 | c131 | 9
Any idea how to do that? (without trying to sort on the lookup column,
whose values can be random outside this test)
Best regards,
Philippe Lang
