Select stmt created by rails paginating_find plugin works inconsistently

Question

I am using the ruby on rails plugin paginating_find to page through data in a table with 1563 records.
The paging works fine for some pages, but after paging through a few pages the same set of records are returned regardless of the paging parameters.
From the rails log I see that the following statement is executed:
select project_id, raw_rnum_ from (select raw_sql_.*, rownum raw_rnum_ from (SELECT * FROM MD_PROJECT ORDER BY last_revision_date asc) raw_sql_ where rownum <= 1523) where raw_rnum_ > 1513;
If I run this in sqlplus, the statement returns 10 records as expected:
SQL> select project_id, raw_rnum_ from (select raw_sql_.*, rownum raw_rnum_ from (SELECT * FROM MD_PROJECT ORDER BY last_revision_date asc) raw_sql_ where rownum <= 1523) where raw_rnum_ > 1513;
PROJECT_ID RAW_RNUM_
1039 1514
1423 1515
1422 1516
1421 1517
1411 1518
1410 1519
1409 1520
1408 1521
1407 1522
1406 1523
10 rows selected.
If I change the where clause and run again, the same records are returned (I would expect the previous 10 records):
SQL> select project_id, raw_rnum_ from (select raw_sql_.*, rownum raw_rnum_ from (SELECT * FROM MD_PROJECT ORDER BY last_revision_date asc) raw_sql_ where rownum <= 1513) where raw_rnum_ > 1503;
PROJECT_ID RAW_RNUM_
1039 1504
1423 1505
1422 1506
1421 1507
1411 1508
1410 1509
1409 1510
1408 1511
1407 1512
1406 1513
Note that this behaviour occurs after paging a few pages, starting from the first or from the last page. Also not that I order by a column of type date.
Now, if I change the statement to order by a non-date type column, it works as expected:
SQL> select project_id, raw_rnum_ from (select raw_sql_.*, rownum raw_rnum_ from (SELECT * FROM MD_PROJECT order by project_id) raw_sql_ where rownum <= 1523) where raw_rnum_ > 1513;
PROJECT_ID RAW_RNUM_
2461 1514
2462 1515
2463 1516
2464 1517
2465 1518
2466 1519
2468 1520
2497 1521
2515 1522
2522 1523
10 rows selected.
SQL> select project_id, raw_rnum_ from (select raw_sql_.*, rownum raw_rnum_ from (SELECT * FROM MD_PROJECT order by project_id) raw_sql_ where rownum <= 1513) where raw_rnum_ > 1503;
PROJECT_ID RAW_RNUM_
2434 1504
2437 1505
2438 1506
2439 1507
2440 1508
2441 1509
2442 1510
2443 1511
2444 1512
2445 1513
10 rows selected.
SQL>
The records returned are now the next 10 records as expected.
The Oracle version is Oracle Database 10g Express Edition Release 10.2.0.1.0 (on linux), and I also find the same behaviour on Oracle Database 10g Release 10.2.0.3.0 (on windows).
Any comments are welcome...
Thanks,
Bjørn

Answer 1

I think the problem is that the rownum is created in a different select than where you have your order by criteria.
Besides what Nigel said.
This should work (not sure how to put it into the rails framework):
select project_id, raw_rnum_
      from (select *
            from (SELECT MD_PROJECT.*, rownum raw_rnum_
                  FROM MD_PROJECT
                  ORDER BY last_revision_date asc, project_id
                  ) raw_sql_
            where raw_rnum_ <= 1523
      where raw_rnum_ > 1513; Of cause the two outer selects could be joined to one.
Message was edited by:
Sven W.