Oracle query to obtain batches of rows - oracle

Question

So here is my problem: I need to get batches of rows (select statements) for a migration to another database (other then oracle).
Suggested solution: I take batches of rows (using rowid maybe?) example:
batch1: 0-10000,
batch2: 10000 - 20000,
batchn: 10000(n) - 10000(n+1)
So what should my query be?
batch1: select * from table_name where rownum >= 0 and rownum < 10000,
batch2: select * from table_name where rownum >= 10000 and rownum < 20000,
batch n: select * from table_name where rownum >= 10000*n and rownum < 10000*(n+1)
This does not work, (only the first select will work).
PS, I am pulling this data from a nodejs app, and thus I am sending in these batch queries in a for loop.

Answer 1

To illustrate my comment:
-- Between rows --
SELECT * FROM
( SELECT deptno, ename, sal, ROW_NUMBER() OVER (ORDER BY ename) Row_Num
FROM scott.emp
)
WHERE Row_Num BETWEEN 5 and 10
/
You may replace between operator with <= and >= if necessary.
Here's what I see in output:
DEPTNO ENAME SAL ROW_NUM
20 FORD 3000 5
30 JAMES 950 6
20 JONES 2975 7
10 KING 5000 8
30 MARTIN 1250 9
10 MILLER 1300 10

Answer 2

Using rownum is not a great idea, because there's no guarantee that the same rows will be assigned the same rownum values in different queries.
If the table has any combination of columns that uniquely identify a row, it is better to generate a ranking based on that and use that ranking to identify batches of rows. For example:
SELECT * FROM (
SELECT table.*, RANK() OVER (ORDER BY column1, column2) as my_rank
FROM table
)
WHERE my_rank >= 10000 AND my_rank < 20000
This will work with any range, and will be reproducible as long as the values in the columns used do not change and uniquely identify a row. (Actually, I think this would be usable even if they do not uniquely identify a row, as long as they work to break the rows into small enough batches.)
The downside is that MY_RANK will be included in the output. You can avoid that by explicitly listing the columns you do want to select; or it may be easier to filter it out when you are loading the data into the other database.

Answer 3

If you want to preserve the rowids, use the following SQL. This SQL took 4 minutes, 20 seconds to run against a 218 million row table on a 2 CPU server with 18 GB devoted to the DB.
CREATE TABLE rowids
AS
WITH
aset
AS
(SELECT ROWID AS row_id, row_number () OVER (ORDER BY ROWID) r
FROM amiadm.big_table)
SELECT *
FROM aset
WHERE MOD (r, 10000) = 0;
After creating this table, loop through it with the following:
BEGIN
FOR recs
IN ( SELECT row_id
, LAG (row_id) OVER (ORDER BY row_id) prev_row_id
, LEAD (row_id) OVER (ORDER BY row_id) next_row_id
FROM rowids
ORDER BY row_id)
LOOP
IF prev_row_id IS NULL
THEN
SELECT *
FROM big_table
WHERE ROWID <= recs.row_id;
ELSIF next_row_id IS NULL
THEN
SELECT *
FROM big_table
WHERE ROWID > row_id;
ELSE
SELECT *
FROM big_table
WHERE ROWID > prev_row_id
AND ROWID <= row_id;
END IF;
END LOOP;
END;