[jira] [Commented] (OPENJPA-2416) setFirstResult/setMaxResults (Paging) with Oracle

["Ognjen Blagojevic (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/OPENJPA-2416?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13723920#comment-13723920 ] 

Ognjen Blagojevic commented on OPENJPA-2416:
--------------------------------------------

I think this is not related to OpenJPA per se. Most RDBMSs handle LIMIT and OFFSET the same way as OpenJPA handles setFirstResult and setMaxResults. 

You shouldn't use setFirstResult/setMaxResults without providing unique ordering yourself.
                
> setFirstResult/setMaxResults (Paging) with Oracle
> -------------------------------------------------
>
>                 Key: OPENJPA-2416
>                 URL: https://issues.apache.org/jira/browse/OPENJPA-2416
>             Project: OpenJPA
>          Issue Type: Improvement
>          Components: query
>    Affects Versions: 2.1.1
>            Reporter: Andreas Mader
>
> We are using OpenJPA with Oracle 11g Database. For Paging we use setFirstResult and setMaxResults to Page through the result set.
> Lets take an example: PageSize 25.
> first Statement: firstResult: 0; maxResults: 26 (1 more to check if it is truncated)
> SQL generated: 
> SELECT * FROM ([my statement]) WHERE ROWNUM <= 26
> second Statement: firstResult: 25; maxResults: 26
> SQL generated: 
> SELECT * FROM (SELECT r.*, ROWNUM RNUM FROM ([my statement]) r WHERE ROWNUM <= 50) WHERE RNUM > 25
> The way limiting the resultset for paging is sometimes not correct. The last result of the statement should be equal to the first result of the new page - but it isn't always. If the sorting is done on a non-unique column in the database, there are different sortings in the resultset of these two statements. I don't know why it is done this way, I would prefer the following statement (this works for all values of firstResult and maxResults with non-unique sort column):
> SELECT outer.* FROM (
>   SELECT ROWNUM rn, inner.* FROM 
>      ([my statement])
>   inner)
> outer WHERE outer.rn > 25 AND outer.rn <= 50

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