Postgresql copy data within the tree table - sql

Question

I have table with tree structure, columns are id, category, parent_id
Now I need a copy a node and its child's to a another node, while copying, the category must be same, but with new id and parent_id..
My input will be node to copy & destination node to copy
I have explained the tree structure in the image file..
i need a function to do so..,
PostgreSQL version 9.1.2
Column | Type | Modifiers
-----------+---------+-------------------------------------------------
id | integer | not null default nextval('t1_id_seq'::regclass)
category | text |
parent_id | integer |
Indexes:
"t1_pkey" PRIMARY KEY, btree (id)
Foreign-key constraints:
"fk_t1_1" FOREIGN KEY (parent_id) REFERENCES t1(id)
Referenced by:
TABLE "t1" CONSTRAINT "fk_t1_1" FOREIGN KEY (parent_id) REFERENCES t1(id)

Answer 1

(tested under PostgreSQL 8.4.3)
The following query assigns new IDs to the sub-tree under node 4 (see the nextval) and then finds the corresponding new IDs of parents (see the LEFT JOIN).
WITH RECURSIVE CTE AS (
SELECT *, nextval('t1_id_seq') new_id FROM t1 WHERE id = 4
UNION ALL
SELECT t1.*, nextval('t1_id_seq') new_id FROM CTE JOIN t1 ON CTE.id = t1.parent_id
)
SELECT C1.new_id, C1.category, C2.new_id new_parent_id
FROM CTE C1 LEFT JOIN CTE C2 ON C1.parent_id = C2.id
Result (on your test data):
new_id category new_parent_id
------ -------- -------------
9 C4
10 C5 9
11 C6 9
12 C7 10
Once you have that, it's easy to insert it back to the table, you just have to be careful to reconnect the sub-tree root with the appropriate parent (8 in this case, see the COALESCE(new_parent_id, 8)):
INSERT INTO t1
SELECT new_id, category, COALESCE(new_parent_id, 8) FROM (
WITH RECURSIVE CTE AS (
SELECT *, nextval('t1_id_seq') new_id FROM t1 WHERE id = 4
UNION ALL
SELECT t1.*, nextval('t1_id_seq') new_id FROM CTE JOIN t1 ON CTE.id = t1.parent_id
)
SELECT C1.new_id, C1.category, C2.new_id new_parent_id
FROM CTE C1 LEFT JOIN CTE C2 ON C1.parent_id = C2.id
) Q1
After that, the table contains the following data:
new_id category new_parent_id
------ -------- -------------
1 C1
2 C2 1
3 C3 1
4 C4 2
5 C5 4
6 C6 4
7 C7 5
8 C8 3
9 C4 8
10 C5 9
11 C6 9
12 C7 10