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From "Stefan Zeiger (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-5911) WHERE condition getting pushed into sub-query with FETCH
Date Tue, 28 Aug 2012 11:38:07 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5911?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13443082#comment-13443082
] 

Stefan Zeiger commented on DERBY-5911:
--------------------------------------

Note that this attempt at a work-around suffers from the same issue:

    select cof_name, price from (
      select row_number() over() as rownum, COF_NAME, PRICE from (select * from COFFEES order
by COF_NAME) t
    ) as t where t.rownum <= 2 and t.PRICE < 10

                
> WHERE condition getting pushed into sub-query with FETCH
> --------------------------------------------------------
>
>                 Key: DERBY-5911
>                 URL: https://issues.apache.org/jira/browse/DERBY-5911
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.9.1.0
>         Environment: Tested with Derby 10.9.1.0 on Windows 7 x64, Java 1.6.0_27-b07 server
>            Reporter: Stefan Zeiger
>
> Derby pushes query conditions down into subqueries with FETCH limits, thus creating wrong
results. Take the following snippet:
>     CREATE TABLE COFFEES (COF_NAME VARCHAR(254),PRICE INTEGER);
>     
>     INSERT INTO COFFEES (COF_NAME,PRICE) VALUES ('Colombian',       5);
>     INSERT INTO COFFEES (COF_NAME,PRICE) VALUES ('French_Roast',    5);
>     INSERT INTO COFFEES (COF_NAME,PRICE) VALUES ('Colombian_Decaf', 20);
>     
>     select COF_NAME, PRICE from COFFEES order by COF_NAME fetch next 2 rows only;
>     
>     select * from (
>       select COF_NAME, PRICE from COFFEES order by COF_NAME fetch next 2 rows only
>     ) t where t.PRICE < 10;
> The first query correctly returns the rows (Colombian,5), (Colombian_Decaf,20).
> The second query (which filters the result of the first one) returns (Colombian,5), (French_Roast,5).
The row (French_Roast,5) should not be there since it is not a result of the first query.
It shows up because (supposedly) the filter condition has been evaluated before the fetch
limit.

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