Fill table with data based on other table? - sql

Question

I have 2 tables in Oracle database: document and document_closure.
document:
- id
- name
- parent_id
document_closure:
- id
- parent_id
- child_id
- level
document table has a lot of data (10k~20k). document_closure is empty.
Question: How to fill document_closure table with data based on document table. What sql script needs to be my that task?
Lets say I have such tree. Example:
A
|
- B
|
- C
document table:
id | parent_id | name
1 | | A
2 | 1 | B
3 | 2 | C
Finally document_closure must be:
id | parent_id | child_id | level
1 | 1 | 1 | 0
2 | 2 | 2 | 0
3 | 3 | 3 | 0
4 | 1 | 2 | 1
5 | 2 | 3 | 1
6 | 1 | 3 | 2

Answer 1

While parent_id and name fields in document_closure are the same coming from document table, you didn't mention what to put in the name field...
However assuming you can use the same (or null) value for the name field you just need an INSERT INTO SELECT statement like this
INSERT INTO table2 (column1, column2, column3, ...) SELECT column1, column2, column3, ... FROM table1 WHERE condition;
that copies data from document table and inserts them into document_closure table. In your case you just need the following SQL:
INSERT INTO document_closure (id,parent_id) SELECT id,parent_id FROM document;
and you'll have all your records in document table copied in document_closure table.

Answer 2

This can be done USING Oracle's connect by for hierarchical queries. This comes with a number of handy functions, including level to indicate how far down the hierarchy you are and connect_by_root() which returns the root value of the hierarchy (i.e. the top level value).
The query to generate the data based on the documents table looks something like:
WITH documents AS (SELECT 1 ID, NULL parent_id, 'A' NAME FROM dual UNION ALL
SELECT 2 ID, 1 parent_id, 'B' NAME FROM dual UNION ALL
SELECT 3 ID, 2 parent_id, 'C' NAME FROM dual)
-- end of mimicking a table with your sample data in it.
-- Since you already have this table, you don't need to bother defining the above subquery.
SELECT row_number() OVER (ORDER BY LEVEL, connect_by_root(ID), ID) ID,
connect_by_root(ID) parent_id,
ID child_id,
LEVEL -1 lvl
FROM documents d
CONNECT BY PRIOR ID = parent_id;
ID PARENT_ID CHILD_ID LVL
---------- ---------- ---------- ----------
1 1 1 0
2 2 2 0
3 3 3 0
4 1 2 1
5 2 3 1
6 1 3 2